Display system and light guide

ABSTRACT

A display system including an imager for forming an image, and a projection lens system for projecting the image formed by the imager is described. For each pixel in the plurality of pixels, the imager is configured to emit a cone of light having a central ray having a direction that varies with location of the pixel in the imager. The variation may increase a brightness of an image projected through the projection lens system by at least 30 percent. The display system may include a light guide having a light insertion portion adapted to receive light; a light transport portion disposed to receive light from the light insertion portion; and a light extraction portion disposed to receive light from the light transport portion.

BACKGROUND

An optical system may include a display panel and a lens system thatreceives light from the display panel and directs the light to aviewer's eye.

SUMMARY

In some aspects of the present description, a display system includingan imager for forming an image, and a projection lens system forprojecting the image formed by the imager is provided. The imagercomprises a plurality of discrete spaced apart pixels. For each pixel inthe plurality of pixels, the imager is configured to emit a cone oflight having a central ray which has a direction that varies withlocation of the pixel in the imager. The variation increasing abrightness of an image projected through the projection lens system byat least 30 percent.

In some aspects of the present description, a display system including aprojection lens system having one or more lenses centered on an opticalaxis, a light guide and a spatial light modulator is provided. The lightguide includes a light insertion portion adapted to receive light; alight transport portion disposed to receive light from the lightinsertion portion; and a light extraction portion disposed to receivelight from the light transport portion. The light extraction portion isconfigured to provide a light output central ray direction having anangle with respect to the optical axis that varies with location on anoutput surface of the light extraction portion. The light extractionportion is separated from the light insertion portion along the opticalaxis forming a space between the light extraction portion and the lightinsertion portion. The spatial light modulator is in opticalcommunication with the light extraction portion and the light guide isfolded such that the light extraction portion faces the light insertionportion.

In some aspects of the present description, a display system including aprojection lens system having one or more lenses and having a largestlateral optically active dimension; an imager having a largest lateraloptically active dimension; and a light guide is provided. An imageformed by the imager is projected by the projection lens system. Thelight guide receives light from a light source and includes a lightextraction portion disposed between the projection lens system and theimager. The light extraction portion includes a plurality of discretespaced apart light extraction features for extracting and directing thereceived light toward the imager. The largest lateral optically activedimension of the projection lens system is no more than 80 percent ofthe largest lateral optically active dimension of the imager.

In some aspects of the present description, a light guide including alight insertion portion adapted to receive light; a light transportportion disposed to receive light from the light insertion portionthrough a first fold; and a light extraction portion disposed to receivelight from the light transport portion through a second fold isprovided. The light extraction portion is spaced apart from and facesthe light insertion portion.

In some aspects of the present description, a light guide including alight insertion portion adapted to receive light; a light transportportion disposed to receive light from the light insertion portion; anda light extraction portion disposed to receive light from the lighttransport portion is provided. The light received by the light insertionportion propagates predominately along a first direction. The lighttransport portion has a first segment and the light received by thelight transport portion propagates predominately along a seconddirection in the first segment. The light received by the lightextraction portion propagates predominately along a third direction. Afirst included angle between the first and second directions is at least140 degrees and a second included angle between the first and thirddirections is less than 40 degrees.

In some aspects of the present description, a display system including aprojection lens system and a light guide is provided. The light guideincludes a light insertion portion adapted to receive light, and a lightextraction portion disposed to receive light from the light insertionportion. The light received by the light insertion portion propagatespredominately along a first direction. The light received by the lightextraction portion propagates predominately along a second direction. Anincluded angle between the first direction and the second direction isat least 120 degrees. The light extraction portion includes a pluralityof light extraction features adapted to extract light from the lightextraction portion towards the projection lens system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of an optical system;

FIGS. 1B-1C are cross-sectional views of displays;

FIG. 2A is a cross-sectional view of an optical system;

FIG. 2B is a cross-sectional view of light output from a pixel in areference light emitting system;

FIG. 2C is a cross-sectional view of light output from a pixel in alight emitting system;

FIGS. 3-5 are cross-sectional views of optical systems;

FIGS. 6-8 are schematic cross-sectional views of light emitting systems;

FIG. 9 is a cross-sectional view of a light redirecting layer;

FIG. 10 is a cross-sectional view of a light emitting system;

FIGS. 11A-11B are cross-sectional views of pixels including lightredirecting elements;

FIGS. 12-15 are schematic cross-sectional views of light emittingsystems;

FIG. 16A is a cross-sectional view of an optical system;

FIGS. 16B-16C are cross-sectional and perspective views, respectively,of a display system;

FIGS. 17-22 are cross-sectional views of light emitting systems;

FIG. 23 is a cross-sectional view of a lens system;

FIG. 24 is a cross-sectional view of a light emitting system;

FIG. 25 is a schematic top view of a head-mounted display;

FIGS. 26-28 are schematic cross-sectional views of light guides; and

FIG. 29 is a schematic representation of an included angle between twodirections.

DETAILED DESCRIPTION

Display systems can include a display panel and a lens system thatreceives light from the display panel and transmits at least a portionof the light through an exit pupil of the display system. The lenssystem may include a reflective polarizer, a partial reflector adjacentto and spaced apart from the reflective polarizer, and a quarter waveretarder disposed between the reflective polarizer and the partialreflector. The partial reflector transmits at least some of the lightreceived from the display panel through the reflective polarizer andthrough the exit pupil. Such display systems can provide a wide field ofview in a compact system that can be used in head-mounted displays suchas virtual reality displays, for example. Useful display systems aredescribed in U.S. Provisional Patent Application No. 62/214,049 filedSep. 3, 2015 and hereby incorporated by reference herein to the extentthat it does not contradict the present description.

According to the present description, it has been found that thefraction of light emitted by the display panel that is transmittedthrough the exit pupil can be substantially increased compared toconventional display systems by altering the light output of the displaypanel such that one or both of a direction of the light output or adegree of collimation of the light output is suitably altered. Asdescribed further elsewhere herein, this can be achieved by including alight redirecting layer between the display panel and the partialreflector (for example, by including a light redirecting layer directlyon a surface of the display panel), or by modifying a backlight used toilluminate the display panel.

FIG. 1 is a schematic cross-sectional view of optical system 100including light emitting system 132, lens system 119 and exit pupil 135.Light emitting system 132 is adapted to provide a light output that canbe efficiently utilized by lens system 119. Light emitting system 132may include a light redirecting layer and/or an at least partiallycollimating backlight. Suitable light emitting systems are describedfurther elsewhere herein. Light emitting systems such as light emittingsystem 132 may be pixelated and may be referred to as a pixelated systemor as a pixelated display. Optical system 100 may be a display systemthat can be utilized, for example, in a head-mounted display.

Lens system 119 includes a first optical stack 110 disposed between thelight emitting system 132 and the exit pupil 135, a second optical stack120 is disposed between the first optical stack 110 and the exit pupil135. Each of the first and second optical stacks 110 and 120 may besubstantially planar or may be curved about one or two axes. In someembodiments, each of the first and second optical stacks 110 and 120 areconvex toward the light emitting system 132 along orthogonal first andsecond axes. An x-y-z coordinate system is provided in FIG. 1. Theorthogonal first and second axes may be the x- and y-axes, respectively.

The first optical stack 110 includes a first optical lens 112 havingopposing first and second major surfaces 114 and 116 respectively. Thefirst optical stack 110 includes a partial reflector 117 disposed on thefirst major surface 114. The partial reflector 117 has an averageoptical reflectance of at least 30% in a desired or pre-determinedplurality of wavelengths and may have an average optical transmission ofat least 30% in the desired or pre-determined plurality of wavelengths,which may be any of the wavelength ranges described elsewhere herein. Insome embodiments, the partial reflector 117 has an average opticalreflectance of at least 40% in a desired or pre-determined plurality ofwavelengths and an average optical transmission of at least 40% in thedesired or pre-determined plurality of wavelengths.

The second optical stack includes a second optical lens 122 having firstand second major surfaces 124 and 126. The second optical stack 120includes a reflective polarizer 127 disposed on the second major surface126 and includes a quarter wave retarder 125 disposed on the reflectivepolarizer 127. Quarter wave retarder 125 may be a film laminated on thereflective polarizer 127 or may be a coating applied to the reflectivepolarizer 127. The optical system 100 may include one or more additionalretarders. For example, a second quarter wave retarder may be includedin first optical stack 110 and may be disposed on the second majorsurface 116. The first quarter wave retarder 125 and any additionalquarter wave retarders included in optical system 100 may be quarterwave retarders at at least one wavelength in the pre-determined ordesired plurality of wavelengths. The second optical stack 120 mayalternatively be described as including the second lens 122 and thereflective polarizer 127 disposed on the second lens 122 and the firstquarter wave retarder 125 may be regarded as a separate layer or coatingthat is disposed on the second optical stack 120 rather than beingincluded in the second optical stack 120. In this case, the firstquarter wave retarder 125 may be described as being disposed between thefirst optical stack 110 and the second optical stack 120. In someembodiments, the first quarter wave retarder 125 may not be attached tothe second optical stack 120, and in some embodiments, the first quarterwave retarder 125 is disposed between and spaced apart from the firstand second optical stacks 110 and 120. In still other embodiments, thefirst quarter wave retarder 125 may be disposed on the partial reflector117 and may be described as being included in the first optical stack110 or may be described as being disposed between the first and secondoptical stacks 110 and 120.

One or both of the first and second lenses 112 and 122 may be refractivelenses. A refractive lens is an optical lens that provides a desiredoptical power under transmission. In some embodiments, one or both ofthe first and second lenses 112 and 122 may have low or substantiallyzero optical power under transmission and may provide optical powerunder reflection due to the shape of the lens(es). An optical systemincluding a reflective polarizer and a partial reflector disposedadjacent to an spaced apart from one another may be referred to as afolded optical system since such system provided a folded light path asillustrated in FIG. 1A. An optical system which does not provide such afolded optical path but includes refractive lenses may be described as arefractive optical system.

Light rays 137 and 138 are each transmitted from the light emittingsystem 132 through the exit pupil 135. Light ray 138 may be a centrallight ray whose optical path defines a folded optical axis 140 foroptical system 100, which may be centered on the folded optical axis140.

The light emitting system 132 may include any suitable type of displaypanel including, for example, liquid crystal display (LCD) panels andorganic light emitting diode (OLED) display panels. The display panelmay be substantially flat or planar as illustrated in FIG. 1A, or may becurved as illustrated in FIG. 1B, or may include a plurality of flat orplanar panels disposed at obtuse angles relative to one another as shownin FIG. 1C, for example. FIG. 1B is a schematic cross-sectional view oflight emitting system 132 b which includes display panel 130 b which maybe curved about at least one axis and may be concave toward the lens(es)of the optical system (e.g., the display panel 130 b may be curvedtoward the lenses 112 and 122). Display panel 130 b may be curved in onedimension (a simple curve) or in two dimensions (a compound curve). Forexample, display panel 130 b may be curved in one or both of theorthogonal x- and y-directions. A display panel curved in two dimensionsmay have two different radii of curvature (e.g., the curvature in the x-and y-directions may be different. Such displays may be referred to astoroidal). FIG. 1C is a schematic cross-sectional view of light emittingsystem 132 c which includes substantially planar panels 130 c-1, 130 c-2and 130 c-3. The panels 130 c-1 and 130 c-2 are disposed at an obtuseangle θ1 relative to each other, and the panels 130 c-2 and 130 c-3 aredisposed at an obtuse angle θ2 relative to each other. The panels 130c-1, 130 c-2 and 130 c-3 are disposed to face the lens(es) of theoptical system (e.g., the panels 130 c-1, 130 c-2 and 130 c-3 may facetoward the lenses 112 and 122). Either of the displays panels 130 b and130 c may be used in the light emitting system 132 of FIG. 1A and may beused in other optical systems described elsewhere herein.

Referring again to FIG. 1A, light ray 137 (and similarly for light ray138) is, in sequence, emitted from light emitting system 132,transmitted through second major surface 116 (and any coatings or layersthereon), transmitted through first optical lens 112, transmittedthrough partial reflector 117, transmitted through the quarter waveretarder 125 disposed on the reflective polarizer 127, reflected fromreflective polarizer 127, transmitted back through quarter wave retarder125, reflected from partial reflector 117, transmitted through quarterwave retarder 125, transmitted through reflective polarizer 127,transmitted through second lens 122, and transmitted through exit pupil135. Light ray 137 may be emitted from the light emitting system 132with a polarization state which is rotated to a first polarization stateupon passing through quarter wave retarder 125. The light emittingsystem 132 may include polarization conditioning elements in order toprovide the desired polarization state. Light emitting systems whichemit light in the desired polarization state can result in a highcontrast image. The first polarization state may be a block state forthe reflective polarizer 127. After light ray 137 passes through firstquarter wave retarder 125, reflects from partial reflector 117 andpasses back through quarter wave retarder 125, its polarization state isa second polarization state substantially orthogonal to the firstpolarization state. Light ray 137 can therefore reflect from thereflective polarizer 127 the first time that it is incident on thereflective polarizer 127 and can be transmitted through the reflectivepolarizer 127 the second time that it is incident on the reflectivepolarizer 127.

Other light rays (not illustrated) reflect from the partial reflector117 when incident on the partial reflector 117 in the minus z-directionor are transmitted by the partial reflector 117 when incident on thepartial reflector 117 in the plus z-direction. These rays may exitoptical system 100.

In some embodiments, substantially any chief light ray that is emittedfrom the light emitting system 132 and transmitted through the exitpupil 135 is incident on each of the first optical stack 110 and thesecond optical stack 120 with an angle of incidence less than about 30degrees, less than about 25 degrees, or less than about 20 degrees, thefirst time or each time that the chief light ray is incident on thefirst or second optical stacks 110 or 120. In any of the optical systemsof the present description, substantially any chief light ray emitted bythe light emitting system 132 and transmitted through the exit pupil 134is incident on each of the reflective polarizer and the partialreflector with an angle of incidence less than about 30 degrees, lessthan about 25 degrees, or less than about 20 degrees, the first time oreach time that the chief light ray is incident on the reflectivepolarizer or the partial reflector. If a large majority (e.g., about 90percent or more, or about 95 percent or more, or about 98 percent ormore) of all chief rays emitted by the light emitting system andtransmitted through the exit pupil satisfy a condition, it may be saidthat substantially any chief ray satisfies that condition.

Various factors can cause light to be partially transmitted through thereflective polarizer 127 the first time that light emitted by the lightemitting system 132 is incident on the reflective polarizer 127. Thiscan cause unwanted ghosting or image blurriness at the exit pupil 135.These factors can include performance degradation of the variouspolarizing components during forming and unwanted birefringence in theoptical system 100. The effects of these factors can combine to degradethe contrast ratio and efficiency of the optical system 100. The effectsof these factors on the contrast ratio is described in more detail inU.S. Provisional Patent Application No. 62/214,049 filed Sep. 3, 2015and previously incorporated herein by reference. Such factors can beminimized by using relatively thin optical lenses, which can reduceunwanted birefringence in the lenses, for example, and using thinoptical films, which can reduce optical artifacts arising fromthermoforming optical films, for example. In some embodiments, the firstand second optical lenses 112 and 122 each have a thickness less than 7mm, less than 5 mm, or less than 3 mm, and may have a thickness in arange of 1 mm to 5 mm, or 1 mm to 7 mm, for example. In someembodiments, the reflective polarizer 127 may have a thickness of lessthan 75 micrometers, less than 50 micrometers, or less than 30micrometers. In some embodiments, the contrast ratio at the exit pupil135 is at least 40, or at least 50, or at least 60, or at least 80, orat least 100, or at least 150, or at least 200, or at least 300 over thefield of view of the optical system 100.

A film can be shaped into a compound curve (curved about two orthogonalaxes) by any forming process that deforms or stretches the film into thedesired shape. Suitable forming processes may or may not includeelevated temperatures (thermoforming). Suitable forming processesinclude thermoforming and/or pressurization processing (deforming orstretching the film into the desired shape via the application ofpressure). It has been found that a convex reflective polarizer curvedabout two orthogonal axes that is made by forming a polymeric multilayeroptical film that was uniaxially oriented prior to forming isparticularly advantageous when used in the optical systems of thepresent description. For example, it has been found that the contrastratio can be significantly higher when utilizing such film compared tousing other reflective polarizers. However, other reflective polarizers,such as non-uniaxially oriented multilayer polymeric film reflectivepolarizers or wire grid polarizers, may also be used. In someembodiments, the uniaxially oriented multilayer reflective polarizers isAPF (Advanced Polarizing Film, available from 3M Company, St. Paul,Minn.). In some embodiments, optical systems include a thermoformed APFor a pressure-formed APF and any or substantially any chief ray in theoptical system that is incident on the thermoformed APF or thepressure-formed has a low angle of incidence (e.g., less than about 30degrees, less than about 25 degrees, or less than about 20 degrees).

In some embodiments, a lens system may be utilized that includes asubstantially flat reflective polarizer rather than a curved reflectivepolarizer. In some embodiments, the reflective polarizer is curved aboutone axis and in some embodiments, the reflective polarizer is curvedabout two orthogonal axes. The reflective polarizer may be a multilayeroptical film that is substantially flat or that is substantially curvedabout an axis or about two orthogonal axes. The reflective polarizer maybe a wire grid polarizer that is substantially flat or that issubstantially curved about an axis or about two orthogonal axes.

It has been found that by suitably choosing the shapes of the variousmajor surfaces (e.g., second major surface 126 and first major surface114) that the optical system can provide distortion sufficiently lowthat the image does not need to be pre-distorted. In some embodiments,the light emitting system 132 is adapted to emit an undistorted image.The partial reflector 117 and the reflective polarizer 127 may havedifferent shapes selected such that a distortion of the emittedundistorted image transmitted through the exit pupil 135 is less thanabout 10%, or less than about 5%, or less than about 3%, of a field ofview at the exit pupil 135. The field of view at the exit pupil may begreater than 80 degrees, greater than 90 degrees, or greater than 100degrees, for example.

FIG. 2A is a cross-sectional view of optical system 200 including lenssystem 219, a light emitting system 232 and an exit pupil 235. Lenssystem 219 includes a first optical stack 210 and a second optical stack220. Light emitted from pixels 241, 242 and 243 is illustrated in FIG.2A. Light 247 from pixel 241 includes a chief ray which is transmittedthrough a center of the exit pupil 235. First optical stack 210 includesa lens 212 and a partial reflector disposed on the major surface of lens212 facing exit pupil 235. Second optical stack 220 includes a lens 222and includes a reflective polarizer disposed on the major surface oflens 222 facing the light emitting system 232. A quarter wave retarderis included either disposed on the reflective polarizer facing thepartial reflector or disposed on the partial reflector facing thereflective polarizer. Lens 212 and lens 222 are convex toward lightemitting system 232 about orthogonal axes (e.g., x- and y-axes). Inother embodiments, one or both of the first and second lenses may haveone or more surfaces that are not convex. In some embodiments, one orboth lenses are plano-convex and in some embodiments, one or both lensesare plano-concave. In some embodiments, one lens is plano-convex and theother is plano-concave. In some embodiments, the reflective polarizer isdisposed on a surface that is convex towards the display and thequarter-wave retarder is disposed on a flat surface. The surface that isconvex towards the display can be, for example, the curved surface of aplano-convex lens that is disposed with the curved surface of the lensfacing the display or the curved surface of a plano-concave lens that isdisposed with the flat surface of the lens facing the display.

FIGS. 2B-2C schematically illustrates light emitted from pixel 241 b oflight emitting system 232 b and light emitted by pixel 241 c of lightemitting system 232 c, both corresponding to pixel 241 of light emittingsystem 232 of FIG. 2A. Light from a conventional display panel wouldtypically be emitted in a bundle of light 239 b, which may have aLambertian distribution having a central ray 237 b along a normal to thedisplay panel, for example. In some embodiments, light emitting system232 c includes a light redirecting layer that bends the direction of thecentral ray 237 b towards the direction of the chief ray 247. In thesecases, light emitting system 232 b may be otherwise equivalent to lightemitting system 232 c but without the light redirecting layer. Asdescribed further elsewhere herein, the light redirecting layer mayinclude a plurality of light redirecting elements with each lightredirecting element corresponding to a different group of pixels in adisplay panel. An angle α is illustrated between the chief ray 247 andthe central ray 237 b in FIG. 2B. In some embodiments, for at least onepixel, the light redirecting element corresponding to the pixel reducesthe angle α between the central light ray 247 c and the chief light ray247 emitted by the pixel. In some embodiments, light emitting system 232c includes an at least partially collimating backlight that may direct alight output such that the direction of the central ray 237 c is benttowards the direction of the chief ray 247. As described furtherelsewhere herein, an at least partially collimating backlight produces alight output that is substantially more collimated than a Lambertianoutput. In these cases, light emitting system 232 b may be otherwiseequivalent to light emitting system 232 c but with a backlight thatproduces a substantially Lambertian output with the central ray directednormal to a display surface.

A light redirecting layer that reduces a divergence angle of lightreceived by the light redirecting layer may be said to at leastpartially collimate the light. In some embodiments the angle α isreduced for the light emitting system 232 c relative to the otherwiseequivalent light emitting system 232 b by at least 5 degrees, or atleast 10 degrees, for at least one pixel. In some embodiments the angleα is reduced for the light emitting system 232 c relative to theotherwise equivalent light emitting system 232 b by at least 5 degrees,or at least 10 degrees, for a majority (more than half) of the pixels orfor substantially all of the pixels.

An acceptance angle φ for lens system 219 is illustrated in FIGS. 2B-2C.A greater proportion of light emitted from pixel 241 c of light emittingsystem 232 c is within the acceptance angle φ compared to the proportionof light emitted from pixel 241 b of the otherwise equivalent lightemitting system 232 b that does not include a light redirecting layer oran at least partially collimating backlight. This may be due to one orboth of redirecting the central light ray closer to the chief raydirection and at least partially collimating the light output. A lightemitting system including a plurality of pixels may also be referred toas a pixelated system or a pixelated display and an optical systemincluding the light emitting system and a lens system may be referred toas a display system or as an imaging system. An otherwise equivalentlight emitting system not including a light redirecting component (e.g.,a light redirecting layer or an at least partially collimatingbacklight) may be referred to as a reference pixelated system and thecorresponding display system including the reference pixelated displaysystem may be referred to as an otherwise equivalent display system oras a reference display system. In some embodiments, for each pixel inthe plurality of pixels, the pixelated system is adapted to emit a coneof light having a central ray where the central ray has a direction thatvaries with location of the pixel in the pixelated system such that atotal luminous energy emitted by the pixelated system that is within theacceptance angle of the optical lens system is at least 30 percenthigher, or at least 50 percent higher, or at least 100 percent higher,or at least 200 percent higher, or at least 300 percent higher, or atleast 400 percent higher than that of a reference pixelated system thatis equivalent to the pixelated system except that directions of centralrays of the reference pixelated system are normal to the pixels.

In some embodiments, a brightness of an optical system of the presentdescription at the exit pupil of the optical system is at least 20percent higher, or at least 30 percent higher, or at least 100 percenthigher, or at least 200 percent higher, or at least 300 percent higher,or at least 400 percent higher than that of an otherwise equivalentoptical system not including a light redirecting component. As describedfurther elsewhere herein, the light redirecting component may be a lightredirecting layer, a plurality of light redirecting elements (e.g., amicrolens array or a plurality of prismatic elements), or an at leastpartially collimating backlight.

FIG. 3 is a schematic cross-sectional view of optical system 300including light emitting system 332, exit pupil 335, integral opticalstack 310 including optical lens 312 having first and second majorsurfaces 314 and 316. Light emitting system 332 may be any of the lightemitting systems described elsewhere herein and may include a lightredirecting layer and/or a partially collimating backlight, for example.First quarter wave retarder 325 is disposed on first major surface 314of optical lens 312 and reflective polarizer 327 is disposed on firstquarter wave retarder 325 opposite optical lens 312. Partial reflector317 is disposed on second major surface 316 of optical lens 312 andsecond quarter wave retarder 315 is disposed on partial reflector 317opposite optical lens 312. Optical system 300 may be centered on foldedoptical axis 340 which may be defined by an optical path of a centrallight ray transmitted from the light emitting system 332 through theexit pupil 335. In some embodiments, optical lens 312 is a monolithiccomponent.

Integral optical stack 310 can be made by first forming reflectivepolarizer 327 with first quarter wave retarder 325 coated or laminatedto reflective polarizer 327 and then thermoforming the resulting filminto a desired shape. As described further in U.S. Provisional PatentApplication No. 62/214,049 filed Sep. 3, 2015 and previouslyincorporated herein by reference, the thermoforming tool may have ashape different than the desired shape so that the film obtains thedesired shape after cooling. Partial reflector 317 and second quarterwave retarder 315 may be prepared by coating a quarter wave retarderonto a partial reflector film, by coating a partial reflector coatingonto a quarter wave retarder film, by laminating a partial reflectorfilm and a quarter wave retarder film together, or by first forming lens312 (which may be formed on a film that includes reflective polarizer327 and first quarter wave retarder 325) in a film insert moldingprocess and then coating the partial reflector 317 on the second majorsurface 316 and coating the quarter wave retarder 315 on the partialreflector 317. In some embodiments, a first film including reflectivepolarizer 327 and first quarter wave retarder 325 is provided an asecond film including partial reflector 317 and second quarter waveretarder 315 is provided and then integral optical stack 310 is formedby injection molding lens 312 between the first and second thermoformedfilms in a film insert molding process. The first and second films maybe thermoformed prior to the injection molding step. Other opticalstacks of the present description may be made similarly by thermoformingan optical film, which may be a coated film or a laminate, and using afilm insert molding process to make the optical stack. A second film maybe included in the film insert molding process so that the lens formedin the molding process is disposed between the films.

In alternate embodiments, the first quarter wave retarder 325 may bedisposed on second major surface 316 rather than on first major surface314. The integral optical stack may be formed by thermoforming thereflective polarizer 327 into the desired shape and injection moldinglens 312 onto the reflective polarizer 327. The first quarter waveretarder 325 may then be coated (e.g., spin coated) onto the secondmajor surface 316 and then the partial reflector 317 can be vapor coatedonto the first quarter wave retarder 325. A second quarter wave retardercan be coated onto the partial reflector, or disposed on the displaypanel 332 or positioned between the partial reflector 317 and thedisplay panel 332.

The partial reflector 317 has an average optical reflectance of at least30% in a desired or pre-determined plurality of wavelengths and may havean average optical transmission of at least 30% in the desired orpre-determined plurality of wavelengths, which may be any of thewavelength ranges described elsewhere herein. The first quarter waveretarder 325 and any additional quarter wave retarders included inoptical system 300 may be quarter wave retarders at at least onewavelength in the pre-determined or desired plurality of wavelengths.The multilayer reflective polarizer 327 substantially transmits lighthaving a first polarization state (e.g., linearly polarized in a firstdirection) and substantially reflects light having an orthogonal secondpolarization state (e.g., linear polarized in a second directionorthogonal to the first direction). As described further elsewhereherein, the multilayer reflective polarizer 327 may be a polymericmultilayer reflective polarizer (e.g., APF) or may be a wire gridpolarizer, for example.

Light ray 337 is emitted from the light emitting system 332 andtransmitted through the exit pupil 335. Light ray 337 is transmittedthrough second quarter wave retarder 315 and partial reflector 317 intoand through lens 312. Other light rays (not illustrated) reflect frompartial reflector 317 after passing through second quarter wave retarder315 and are lost from the optical system 300. After making a first passthrough lens 312, the light ray passes through first quarter waveretarder 325 and reflects from reflective polarizer 327. Light emittingsystem 332 may be adapted to emit light having a polarization along thepass axis for reflective polarizer 327 so that after passing throughboth second quarter wave retarder 315 and first quarter wave retarder325 it is polarized along the block axis for the reflective polarizer327 and therefore reflects from the reflective polarizer 327 when it isfirst incident on it. In some embodiments, a linear polarizer isincluded between the light emitting system 332 and the second quarterwave retarder 317 so that light incident on second quarter wave retarder315 has the desired polarization. After light ray 337 reflects fromreflective polarizer 327, it passes back through first quarter waveretarder 325 and lens 312 and is then reflected from partial reflector317 (other light rays not illustrated are transmitted through partialreflector 317) back through lens 312 and is then again incident on thereflective polarizer 327. After passing through first quarter waveretarder 325, reflecting from partial reflector 317 and passing backthrough first quarter wave retarder 325, light ray 337 has apolarization along the pass axis for reflective polarizer 327. Light ray337 is therefore transmitted through reflective polarizer 327 and isthen transmitted through exit pupil 335.

FIG. 4 is a cross-sectional view of optical system 400 including anoptical stack 410, a light emitting system 432 and an exit pupil 435.Light emitting system 432 may be any of the light emitting systemsdescribed elsewhere herein. Light emitted from pixels 441, 442 and 443is illustrated in FIG. 4. Light from pixel 441 includes a chief ray 447which is transmitted through a center of the exit pupil 435. The lightemitting system may include a plurality of light redirecting elementsthat steer and/or partially collimate the light output of a displaypanel so that a greater proportion of the light output it directed intothe acceptance angle of the optical stack 410. Optical stack 410includes a lens 412, a reflective polarizer 427 disposed on the majorsurface of lens 412 facing exit pupil 435, and a partial reflector 417disposed on the major surface of lens 412 facing the image surface 430.A quarter wave retarder is included in optical stack 410 between thereflective polarizer and the lens 412 or between the partial reflectorand the lens 412. Lens 412 is convex toward image surface 430 aboutorthogonal axes (e.g., x- and y-axes).

FIG. 5 is a cross-sectional view of optical system 500 including a lightemitting system 532, a lens system 519 and an exit pupil 535. Lightemitting system 532 may be any of the light emitting systems describedelsewhere herein and may include a display panel and one or more opticalcomponents (e.g., a light redirecting layer and/or a partiallycollimating backlight) adapted to steer and/or partially collimate alight output of the display panel so that a larger proportion of thelight output is within an acceptance angle of the lens system 519.

Lens system 519 includes a first lens 512, an optical stack 520including a second lens 522, and an optical stack 560 including a thirdlens 562. Optical stack 520 includes a partial reflector disposed on themajor surface of second lens 522 facing exit pupil 535 and includes areflective polarizer disposed on the major surface of third lens 562facing the image surface 530. A quarter wave retarder is included eitherin optical system 500 disposed on the reflective polarizer facing thepartial reflector, or disposed on the partial reflector facing thereflective polarizer. The reflective polarizer and the partial reflectorare each convex toward image surface 530 about orthogonal axes (e.g., x-and y-axes). Three bundles of light rays at three locations on the lightemitting system 532 are illustrated. The light rays in each bundle aresubstantially parallel at the exit pupil 535.

FIG. 6 is a schematic side view of light emitting system 632 includingpixelated light source 630 and light redirecting layer 650. Lightemitting system 632 may be used for any of light emitting systems 132,232, 332, 432, and 532, in optical system 100, 200, 300, 400 and 500,respectively, for example. Light redirecting layer 650 may be separatedfrom pixelated light source 630 or may be attached to or integrated withthe pixelated light source 630. Pixelated light source 630 includes aplurality of discrete spaced apart pixels. For example, pixelated lightsource 630 may comprise a high definition display panel having an arrayof 1080 by 1920 pixels. Light from a single pixel is illustrated in FIG.6. Pixel 641 emits a cone of light 639 including central light ray 637.Cone of light 639 is a diverging light having a cone angle of θ₁. Eachportion of light redirecting layer 650 or each light redirecting elementof light redirecting layer 650 receives a cone of light emitted by apixel corresponding to the portion or to the light redirecting elementand transmits received light as a cone of light having one or both ofthe direction of the central ray and the cone angle of the transmittedlight different from that of the received cone of light. In theillustrated embodiment, portion 656 receives cone of light 639 andtransmits the received light as cone of light 649 having central ray647. Cone of light 649 may be a diverging light and has a cone angle ofθ₂. Central ray 647 has a different direction than central ray 637. Issome embodiments, an angle α between the direction of central ray 647and the direction of central ray 639 may be, for example, at least 5degrees or at least 10 degrees, and may be less than 80 degrees, or lessthan 60 degrees, or less than 50 degrees. The cone angle θ₂ may be atleast 2 degrees, or at least 5 degrees, or at least 10 degrees, or atleast 15 degrees lower than the cone angle θ₁. In some embodiments, oneor both of the cone angles θ₁ and θ₂ may be greater than 10 degrees, orgreater than 15 degrees, or greater than 20 degrees, or greater than 30degrees. In some embodiments, the angle α between may be approximatelyzero and the cone angle θ₂ may be substantially less than the cone angleθ1. In some embodiments, the cone angles θ₁ and θ₂ may be approximatelyequal and the angle α between may be substantially greater than zero. Insome embodiments, the angle α may be substantially greater than zero andthe cone angle θ₂ may be substantially less than the cone angle θ₁.

As described further elsewhere herein, light redirecting layer 650 mayinclude a plurality of light redirecting elements with each lightredirecting element corresponding to a group of pixels in the pixelatedlight source 630. The group of pixels includes at least one pixel andmay include a single pixel or a plurality of pixels. In some cases, thedifferent groups of pixels may share one or more common pixels. In othercases, no two different groups of pixels contain a common pixel. A lightredirecting layer may be said to comprise a plurality of lightredirecting elements if the elements are discrete elements or if thelight redirecting layer includes abruptly varying structures such asmicrolenses or Fresnel lenses. In some embodiments, light redirectinglayer 650 may include a plurality of portions with each differentportion corresponding to a different group of pixels in the pixelatedlight source 630. In some embodiments, the portions may be discretelight redirecting elements or a plurality of discrete light redirectingelements. In other embodiments, a light redirecting layer may include aplurality of substantially continuously varying portions withoutabruptly varying structures.

FIG. 7 is a schematic side view of light emitting system 732 includingpixelated light source 730 and light redirecting layer 750. Lightemitting system 732 may be used for any of light emitting systems 132,232, 332, 432, and 532, in optical system 100, 200, 300, 400 and 500,respectively, for example. Pixelated light source 730 includes aplurality of pixels which includes at least first and second pixels 751and 752. Image 751 of pixel 741 is a virtual image located behind thepixel 741 (in the z-direction from the pixelated light source 730).Similarly, image 752 of pixel 742 is a virtual image located behind thepixel 742. Images 751 and 752 are disposed on image surface 755 whichmay be substantially planar or substantially non-planar. Lightredirecting layer 750 includes a plurality of portions, each differentportion corresponding to a different group of pixels in the pixelatedlight source 730. In the illustrated embodiment, each group of pixels isa single pixel. Portion 756 of light redirecting layer 750 correspondsto pixel 741 and portion 757 of light redirecting layer 750 correspondsto pixel 742. Images 751 and 752 may be located at different distancesfrom portions 756 and 757. In some embodiments, light redirecting layer750 includes a plurality of lenses (or other light redirecting elementsas described elsewhere herein) and portions 756 and 757 each include alens. Images 751 and 752 may be located at different distances from therespective lenses in portions 756 and 757. Pixelated light source 730includes a plurality of pixels and may emit a first image. The lightredirecting layer 750 may form a virtual second image of the first imagebehind the plurality of pixels. In other embodiments, the lightredirecting layer may produce a real image instead of a virtual image.This is illustrated in FIG. 8.

FIG. 8 is a schematic side view of light emitting system 832 includingpixelated light source 830 and light redirecting layer 850. Lightemitting system 832 may be used for any of light emitting systems 132,232, 332, 432, and 532, in optical system 100, 200, 300, 400 and 500,respectively, for example. Pixelated light source 830 includes aplurality of pixels which includes at least first and second pixels 851and 852. Image 851 of pixel 841 is a real image located in front ofpixel 841 (in the minus z-direction from the pixelated light source830). Similarly, image 852 of pixel 842 is a real image located in frontof pixel 842. Images 851 and 852 are disposed on image surface 855 whichmay be substantially planar or substantially non-planar. Lightredirecting layer 850 includes a plurality of portions, each differentportion corresponding to a different group of pixels in the pixelatedlight source 830. In the illustrated embodiment, each group of pixels isa single pixel. Portion 856 of light redirecting layer 850 correspondsto pixel 841 and portion 857 of light redirecting layer 850 correspondsto pixel 842. Pixelated light source 830 includes a plurality of pixelsand may emit a first image. The light redirecting layer 850 may form areal second image of the first image in front of the plurality ofpixels. Images 851 and 852 may be located at different distances fromportions 856 and 857. In some embodiments, light redirecting layer 850includes a plurality of lenses (or other light redirecting elements asdescribed elsewhere herein) and portions 856 and 857 each include alens. Images 851 and 852 may be located at different distances from therespective lenses in portions 856 and 857.

An example of a light redirecting layer is illustrated in FIG. 9 whichis a cross-sectional view of light redirecting layer 950 including aplurality of lenses 954 on a layer 930. Layer 930 may be a display panelor an outer layer in a display panel, for example, and the plurality oflenses 954 may be formed directly on the display panel. Alternatively,layer 930 may be a polymer substrate, for example, and light redirectinglayer 950 may be attached or laminated to a display panel. The pluralityof lenses 954, which may be a plurality of microlenses, may be arrangedperiodically with a pitch P. The pitch P may be similar to but largerthan a pitch between pixels in a display panel. The pitch P may beselected such that lenses positioned near the center of the displaypanel have an optical axis that is approximately aligned with acorresponding pixel, while lenses away from the center of the displaypanel have an optical axis that is laterally offset (e.g., offset in aplane of the display panel which may be parallel to the x-y plane ofFIG. 9) from the corresponding pixel. In some embodiments, the offsetincreases monotonically from a center of the display panel to an edge ofthe display panel. The monotonic increase in the offset may be a linearincrease or a non-linear increase.

Light redirecting layers, such as those including microlens arrays, canbe made by a variety of different techniques. Such techniques includesinclude photopolymer reflow, gray scale lithography, laser ablation, dipcoating of curable monomers on patterned hydrophobic/hydrophilicsubstrates, ink jet printing of curable monomers, diamond turning, ionbeam or wet etching, and electrodeposition. Other suitable processesinclude two-photon processes such as those described in U.S. Pat. No.7,583,444 (DeVoe et al.).

FIG. 10 is a schematic side view of light emitting system 1032 whichincludes a plurality of discrete spaced apart pixels 1044 and a lightredirecting layer 1050 which includes a plurality of light redirectingelements 1054. Light redirecting elements 1054 may correspond to lenses954. A lens may be included for all pixels in a display panel or foronly some of the pixels. For example, pixels a region near an opticalaxis of an optical system including the light emitting system 1032 mayoptionally not include light redirecting elements. Light emitting system1032 may be used for any of light emitting systems 132, 232, 332, 432,and 532, in optical system 100, 200, 300, 400 and 500, respectively, forexample. Light redirecting element 1056 receives a cone of light 1039from pixel 1041 and transmits the received light as a cone of light1049. As described further elsewhere herein, the cone of light 1049 mayhave one or both of the cone angle and central ray direction changedfrom that of the cone of light 1039. The plurality of pixels 1044 aredisposed along a surface 1033, which in the illustrated embodiment is asubstantially planar surface. In other embodiments, the surface 1033 maybe curved. For example, a curved display panel (e.g., LCD or OLED panel)may comprise the plurality of pixels. A surface, such as surface 1033,along which pixels are disposed may be referred to as a pixelatedsurface.

The plurality of pixels in FIG. 10 are represented by discrete spacedapart dark lines. In other figures, pixels may be represented by openspaces between dark lines. In FIG. 10, the spaces between the dark linesrepresent gaps between adjacent pixels. Pixels 1044 have a pixel widthw, which may be a width across the pixel along a repeat direction (e.g.,the y-direction in FIG. 10) of the pixels, and a gap g, which may be awidth of the space between adjacent pixels along the repeat direction.In some embodiments, adjacent pixels are spaced apart by about 10percent to about 100 percent of the pixel width (e.g., g/w is in a rangeof about 0.1 to about 1). In some embodiments, the gap between adjacentpixels includes a light absorbing material 1036, which may be, forexample, black chrome. In OLED displays, for example, a light absorbingblack matrix may be included between adjacent pixels as is known in theart. Including a light absorbing material between adjacent pixels canimprove contrast in an optical system including a light emitting systemand a lens system having a partial reflector since light incident on thelens system that is reflected back to the light emitting system can beat least partially absorbed by the light absorbing material. In otherembodiments, the gap between adjacent pixels is substantially lighttransmissive. This may be the case in an at least partially transparentdisplay panel, such as an at least partially transparent OLED displaypanel, for example. In this case, contrast can be improved since lightincident on the lens system that is reflected back to the light emittingsystem can be at least partially transmitted through the light emittingsystem without reflecting back through the lens system which could causea reduction in contrast. In some embodiments, the spacing betweenadjacent pixels may be small. For example, in some embodiments, the gapbetween adjacent pixels is less than 10 percent of the pixel width, orless than 5 percent of the pixel width (e.g., g/w is less than 0.1, orless than 0.05). In some embodiments, the gap, g, between adjacentpixels is less than 2 micrometers, or less than 1 micrometer, or lessthan 0.5 micrometers.

FIG. 11A illustrates a pixel 1142 including a light emitter 1141 and alens 1154 a. The light emitter 1141 emits cone of light 1139 havingcentral ray 1137, and lens 1154 a receives the cone of light 1139 andtransmits the received light as cone of light 1149 having central lightray 1147. Lens 1154 a is centered on optical axis 1140 which islaterally offset from light emitter 1141 by a distance d. Pixel 1142 maycorrespond to the combination of pixel 1041 and light redirectingelement 1056, for example. A light emitting system including a pluralityof the pixels 1142 may be used for any of light emitting systems 132,232, 332, 432, and 532, in optical system 100, 200, 300, 400 and 500,respectively, for example. As described further elsewhere herein, thelateral offset distance d may increase monotonically from a center of adisplay panel to an edge of the display panel.

A light redirecting element may be a lens which may include a sphericalor aspherical portion rotationally symmetric about an optical axis ofthe lens, or may be a prismatic element which may have one or morecurved surfaces. FIG. 11B shows a lens or light redirecting element 1154b which may be used in place of lens 1154 a. In some embodiments, aplurality of light redirecting element 1154 b may be arrangedperiodically with a pitch selected to match a corresponding pixel pitchin a pixelated light source. The pixels in the pixelated light sourcemay be disposed along a pixelated surface 1133 which may be asubstantially planar surface or a substantially curved surface. Lightredirecting element 1154 b includes opposing first and second sides 1131a and 1131 b and a curved surface 1131 c connecting the first and secondsides 1131 a and 1131 b. Light redirecting element 1154 b can bedescribed as having a lens portion 1194 which includes the curvedsurface 1131 c and a prismatic base portion 1196. The base portion 1196may have a square or rectangular cross-section, for example, in a planeparallel to surface 1133 containing the light emitter 1141 b (a planeparallel to the x-y plane of FIG. 11B). First and second sides 1131 aand 1131 b may be planar faces, for example. The base portion 1196 mayhave a circular cross-section, for example, in a plane parallel to thesurface 1133. First and second sides 1131 a and 1131 b may then beopposite sides of a cylindrical base 1196. In some embodiments, thefirst side 1131 a extends further from the surface 1133 along a normalto the surface 1133 (normal along the minus z-direction) than the secondside 1131 b. A prismatic element may be understood to include a prismcomponent (e.g., base portion 1196) and a lens component (e.g., curvedsurface 1131 c) where the lens component has at least one convexsurface.

Light emitter 1141 b emits a first cone of light having a central lightray 1137 b. The first cone of light is received by light redirectingelement 1154 b and transmitted as a second cone of light having centrallight ray 1147 b. Central light ray 1137 a may be along a first coneaxis and central light ray 1137 b may be along a second cone axis. Anangle α between the first and second cone axes may be at least 5 degreesor at least 10 degrees, or may be in a range of 5 degrees to 50 degreesor to 60 degrees, for example. The light redirecting element 1154 b maybe asymmetric about the first cone axis. The curved surface 1131 c maybe rotationally asymmetric about the first cone axis and substantiallyrotationally symmetric about axis 1193 which is not parallel to thefirst cone axis and may not be parallel to the second cone axis.

In some embodiments, an imaging system includes a plurality of lightemitters 1141 b and a plurality of light redirecting elements 1154 b.The light emitter 1141 b together with the corresponding lightredirecting element 1154 b may be referred to as a pixel and an imagingsystem may include a plurality of such pixels. In some embodiments, fora first pixel in the plurality of pixels, a first angle between thefirst and second cone axes is greater than 5 degrees, or greater than 10degrees, and for a different second pixel in the plurality of pixels, asecond angle between the first and second cone axes is greater than 5degrees, or greater than 10 degrees, and is different from the firstangle. In some embodiments, for a majority of pixels in the plurality ofpixels, the first and second cone axes are not parallel and in someembodiments, for a majority of pixels in the plurality of pixels, anangle between the first and second cone axes is at least 5 degrees, orat least 10 degrees, or in a range of 5 degrees to 50 degrees or to 60degrees.

FIG. 12 is a schematic side view of light emitting system 1232 includinga display panel 1230 comprising a plurality of discrete spaced apartpixels and disposed to receive light from backlight 1236 and transmitpatterned light through light redirecting layer 1250. Display panel 1230may be any suitable spatial light modulator such as a liquid crystaldisplay (LCD) panel, or a grating based modulator, or an interferencebased modulator, or an electrochromic modulator, or an electrophoreticmodulator. In other embodiments, an organic light emitting display(OLED) comprises the plurality of discrete spaced apart pixels and thebacklight 1236 may be omitted. Light emitting system 1232 may be usedfor any of light emitting systems 132, 232, 332, 432, and 532, inoptical system 100, 200, 300, 400 and 500, respectively, for example.

In some embodiments, backlight 1236 may be an at least partiallycollimating backlight. A backlight may be said to be an at leastpartially collimating backlight if the light output from the backlightis substantially more collimated than a Lambertian light output. In someembodiments, at least 50 percent of a lumen output of the at leastpartially collimating backlight is in a 60 degree, or a 50 degree, or a40 degree, or a 30 degree, or a 25 degree, or a 20 degree full widthcone. In some embodiments, at least 60 percent of a lumen output of theat least partially collimating backlight is in a 70 degree, or a 60degree, or a 50 degree, or a 40 degree, or a 30 degree, or a 25 degreefull width cone.

FIG. 13 is a schematic side view of light emitting system 1332 includingpixels 1341, 1342, and 1343. Light emitting system 1332 may be used forany of light emitting systems 132, 232, 332, 432, and 532, in opticalsystem 100, 200, 300, 400 and 500, respectively, for example. Each pixelis adapted to emit a cone of light having a central ray and a coneangle. Pixel 1341 emits cone of light 1349 having central light ray 1347which in the illustrated embodiment is parallel to optical axis 1340,which may be an optical axis of a lens system disposed to receive lightfrom light emitting system 1332. Pixel 1342 emits a cone of light havinga full width cone angle θ. Light emitting system 1332 may include adisplay panel with a light redirecting layer adapted to reduce the coneangle of light emitted by the display panel, which may be an LCD or anOLED display panel, for example. In other embodiments, an at leastpartially collimating backlight may be used with a display panel toproduce an output with a lowered cone angle compared to that producedwith a conventional backlight. For example, an at least partiallycollimating backlight may produce a light output such that at least 50percent of the lumen output is in a 50 degree full width cone or in anyof the ranges described elsewhere herein for a partially collimatingbacklight. A light redirecting layer may be included to further reducethe cone angle or the light redirecting layer may be optionally omitted.In the illustrated embodiment, the light output direction of each of thepixels 1341, 1342 and 1343 is substantially parallel to the optical axis1340. In other embodiments, the light redirecting layer and/or the atleast partially collimating backlight may alter the direction of lightemitted from the light emitting system. This is illustrated in FIGS.14-15.

FIG. 14 is a schematic side view of light emitting system 1432 includingpixels 1441, 1442, and 1443. Light emitting system 1432 may be used forany of light emitting systems 132, 232, 332, 432, and 532, in opticalsystem 100, 200, 300, 400 and 500, respectively, for example. Each pixelemits a cone of light having a cone angle and a central ray. Pixel 1441emits cone of light 1449 having a central ray 1447 emitted along adirection making an angle α to the optical axis 1440 of the lightemitting system 1432 or of a lens system disposed to receive light fromlight emitting system 1432. Pixel 1442 emits a cone of light having acone angle θ. Light from each of pixels 1441 and 1443 is bent towardoptical axis 1440, while light from pixel 1442 is emitted substantiallyalong optical axis 1440. In some embodiments, light from each of pixels1441, 1442, and 1443 are at least partially collimated. In otherembodiments, light from the pixels may have a direction altered withoutbeing at least partially collimated. In some embodiments, an at leastpartially collimated backlight is used to produce at least partiallycollimated light output from light emitting system 1432. In someembodiments, a first portion of the backlight is configured to emitlight at least partially collimated in a first direction and a differentsecond portion of the backlight is configured to emit light at leastpartially collimated in a second different direction. For example, lightfrom the backlight at a location corresponding to pixel 1441 may be atleast partially collimated along the direction of central ray 1447 andlight from the backlight at a location corresponding to pixel 1442 maybe at least partially collimated along a direction parallel to theoptical axis 1440. In some embodiments, light from the at leastpartially collimated backlight may be partially collimated along adirection which varies smoothly across the emitting surface of thebacklight.

FIG. 15 is a schematic side view of light emitting system 1532 includingpixels 1541, 1542, and 1543. Each pixel emits a cone of light having acone angle and a central ray. Pixel 1541 emits cone of light 1549 havinga central ray 1547 emitted along a direction making an angle α to theoptical axis 1540 of the light emitting system 1532 or of a lens systemdisposed to receive light from light emitting system 1532. Pixel 1542emits a cone of light having a cone angle θ. Light from each of pixels1541 and 1543 is bent away optical axis 1540, while light from pixel1542 is emitted substantially along optical axis 1540. In someembodiments, light from each of pixels 1541, 1542, and 1543 are at leastpartially collimated. In other embodiments, light from the pixels mayhave a direction altered without being at least partially collimated. Insome embodiments, an at least partially collimated backlight is used toproduce at least partially collimated light output from light emittingsystem 1532 as further described in connection to FIG. 14.

FIG. 16A is a cross-sectional view of optical system 1600 including lenssystem 1619, and light emitting system 1632 which includes liquidcrystal display panel 1630 and backlight 1636 which is an at leastpartially collimating backlight and may be adapted to provide an outputdirection that varies with location. Backlight 1636 includes light guide1663 which includes collimating optical element 1660 and lightextraction element 1665 having a surface 1667 structured such that lightis extracted from the light guide 1663 as an at least partiallycollimated light. Backlight 1636 further includes light source 1661which is configured to inject light into collimating optical element1660, and back reflector 1668 disposed adjacent light extraction element1665. Light source 1661 may be any suitable light source such as a lightemitting diode (LED) or a plurality of LEDs. Light from the light source1661 may be at least partially collimated as it passes throughcollimating optical element 1660 by virtue of the tapered geometry ofthe collimating optical element 1660. Light is extracted from lightextraction portion 1665 towards back reflector 1668 and the light isthen reflected from the back reflector 1668 and is transmitted throughthe light extraction portion 1665 as an at least partially collimatedlight along desired output directions towards lens system 1619.

In some embodiments, an at least partially collimating backlight that isadapted to provide an output direction that varies with location iscombined with a light redirecting layer. In such embodiments, backlightprovides an output that is partially turned towards a desired directionto be utilized by the lens system and the light redirecting layerreceives this partially turned light and transmits light in a directionmore closely matched to the desired direction for the lens system.

Collimating element 1660 is a light insertion portion of the light guide1663. Light guide 1663 further a light transport portion 1664 disposedto receive light from the collimating optical element 1660 through firstfold 1671 and to transport light to the light extraction element 1665through second fold 1674. Structured surface 1667 of light extractionelement 1665 may include light extractors oriented to produce lightoutput along desired output directions. The surface can be suitablystructured by using a structured stamping tool, such as a structurednickel stamping tool, for example. Suitable stamping tools can beprepared by machining, such as by single point diamond machining.Exemplary diamond turning systems and methods can include and utilize afast tool servo (FTS) as described in, for example, PCT PublishedApplication No. WO 00/48037 (Campbell et al.), and U.S. Pat. No.7,350,442 (Ehnes et al.) and U.S. Pat. No. 7,328,638 (Gardiner et al.).An at least partially collimated backlight may include gratings adaptedto produce light output along desired output directions. Such backlightsare described by Fattal et al., “A multi-directional backlight for awide-angle, grasses-free three dimensional display”, Nature, Vol. 495,pp. 348-351, Mar. 21, 2013. In some embodiments, structured surface 1667may include a series of steps 1666 with sloped portions 1669 between thesteps as described, for example, in U.S. 2013/0321913 (Harold et al.)which is hereby incorporated herein by reference to the extent that itdoes not contradict the present description. Steps 1666 and slopedportions 1669 in structured surface 1667 can be formed by machining, forexample. The sloped portions 1669 cause light to be extracted from thelight extraction element 1665. The distribution of output directions ofsuch backlights can be adjusted by adjusting the distribution of slopesof the sloped portions 1669 between the steps 1666. In some embodiments,the steps have a curved shape as described further elsewhere herein(see, e.g., FIG. 16C).

Optical system 1600 has an exit pupil 1635 and further includes opticalpolarizer 1670 which may be a reflective polarizer, an absorptivepolarizer, a combination of an absorptive and reflective polarizer, ormay optionally be omitted.

Lens system 1619 includes first and second optical lenses 1610 and 1620.First lens 1610 includes a major surface 1614 upon which is disposed apartial reflector having an average optical reflectance of at least 30%in a desired plurality of wavelengths as described elsewhere herein.Second lens 1620 includes a major surface 1626 upon which is disposed areflective polarizer, which may be a thermoformed or pressure-formedreflective polarizer and may be a polymeric multilayer reflectivepolarizer or a wire grid polarizer, for example. A quarter-wave retardermay be disposed on the reflective polarizer.

Any of optical systems 100, 200, 300, 400, 500 or 1600 for example, maybe referred to as a display system or as an imaging system. Any of theseoptical systems may be used in a head-mounted display such as a virtualreality display.

FIGS. 16B and 16C are cross-sectional and perspective views,respectively, of display system 1600 b including an imager 1630 b forforming an image and a projection lens system 1619 b for projecting theimage formed by the imager 1630 b. The imager 1630 b includes aplurality of pixels. For each pixel in the plurality of pixels, theimager is configured to emit a cone of light having a central ray. Thecentral ray has a direction that varies with location of the pixel inthe imager 1630 b by virtue of the geometry of the light extractionelement 1665. In some embodiments, the variation of the central raydirection increases a brightness of an image projected through theprojection lens system by at least 30 percent, or at least 50 percent orat least 100 percent, or at least 200 percent. The image projectedthrough the projection lens is a patterned light that may or may not bein focus throughout the image. For example, the image projected throughthe projection lens may have a central portion forming an in-focus imageand a peripheral portion which may not be in focus. The projection lenssystem 1619 b may be a refractive lens system as illustrated in FIG. 16Bor may be a folded optical system including first and second partialreflectors adjacent to and spaced apart from each other. For example, insome embodiments, the projection lens system 1619 b corresponds to thelens system 119 and the first partial reflector corresponds to partialreflector 117 while the second partial reflector corresponds toreflective polarizer 127. In some embodiments, the projection lenssystem 1619 b has an acceptance angle and the variation in the centralray direction increases light emitted by the imager 1630 b that iswithin the acceptance angle by at least 30 percent, or at least 50percent or at least 100 percent, or at least 200 percent.

In some embodiments, the projection lens system 1619 b has a largestlateral optically active dimension D1 that is less than about 80 percent(or less than about 60%, or less than about 50%, less than about 40%) ofa largest lateral optically active dimension D2 of the imager 1630 b.The largest lateral optically active dimension of a component refers tothe largest lateral dimension, which is the largest dimension in the x-yplane of FIG. 16B, of the portion of the component which is opticallyutilized in forming the output of the display system 1600 b. Forexample, a pixelated display panel typically has a rectangular area ofpixels that is optically active with some border region around therectangular area of pixels that is not optically active. The largestlateral optically active dimension is the diagonal of the rectangulararea of pixels in this case. As another example, a lens may have acircular area that receives and transmits light and the diameter of thiscircular area is the largest lateral optically active dimension in thiscase.

The display system 1600 b includes a light guide 1663 having a lightinsertion portion 1660 b and a light extraction portion 1665 b inoptical communication with the light insertion portion 1660 b and withthe imager 1630 b. The light guide 1663 b is folded such that such thatthe light extraction portion 1665 b faces the faces the light insertionportion 1660 b. The light guide 1663 b includes a light transportportion 1664 b configured to receive light from the light insertionportion 1660 b from first fold 1671 b and transport the light to thelight extraction portion 1665 b through second fold 1673 b. The imager1630 b may be a reflective spatial light modulator (e.g., a liquidcrystal on silicon (LCoS) panel) disposed between the light extractionportion 1665 b and the light insertion portion 1660 b. Alternatively,the imager may be a transmissive spatial light modulator disposedproximate the light extraction portion opposite the light insertionportion as illustrated in FIG. 16A. In the embodiment of FIG. 16B, lightis extracted from light extraction portion 1665 b as an at leastpartially collimated light towards imager 1630 b which reflects animaged light back through light extraction portion 1665 b towards lenssystem 1619 b.

Lens system 1619 b has an optical axis 1640 b (parallel to z-axis). Thelight insertion portion 1660 b and the light extraction portion 1665 bare spaced apart along an optical axis 1640 b of the lens system 1619 b.The optical axis 1640 b intersects the light insertion portion 1660 band the light extraction portion 1665 b.

In some embodiments, structured surface 1667 b includes a series ofsteps 1666 b with sloped portions 1669 b between the steps 1666 b asdescribed for structured surface 1667, steps 1666 and slope portions1669 of FIG. 16A. Steps 1666 or 1666 b may be described as discretespaced apart light extraction features. Other discrete spaced apartlight extraction features suitable for extracting light from the lightextraction portion can be used in place of the steps. In someembodiments, the shape of the light extraction features concentrateslight toward the imager by a combination of curvature around the z-axis,which concentrates light along the x-axis, and changes in angle of theextraction features along the y-axis, which concentrates light along they-axis. The extraction features may be uncoated material, relying ontotal internal reflection (TIR) to extract light, or may be coated witha metallic or dielectric reflector. Alternatively, the entire extractingsurface 1667 or 1667 b may be coated with a reflective polarizer. Thiscan be created through a MacNeille polarizer, a wire grid polarizer, ora polymeric multilayer optical film reflective polarizer such as APF orDual Brightness Enhancement Film (DBEF) available from 3M Company, StPaul, Minn. The reflective polarizer can be shaped to conform to theextracting elements. This can be done by, for example, applying a thinlayer of an adhesive to the structured surface 1667 or 1667 b, andapplying a reflective polarizer film (such as APF) to the surface withheat and/or pressure to conform the film to the structured surface. Oneor more surfaces of the light guide 1663 or 1663 b may have a low indexcoating with the refractive index of the coating being able to maintainTIR conditions within the light guide. In some embodiments, the lowindex coating has a refractive index about 0.05 to 0.2 lower than therefractive index of the light guide (unless specified differently,refractive index refers to the refractive index as measured at 532 nm).The low index coating may be optically thick and may have a physicalthickness of at least 0.5 micrometers or at least 1 micrometer, forexample.

Other suitable light guides suitable for use in optical system 1600 ordisplay system 1600 b are illustrated in FIGS. 26-28.

FIG. 26 is a schematic cross-sectional view of light guide 2663including a light insertion portion 2660 adapted to receive light 2638;a light transport portion 2664 disposed to receive light from the lightinsertion portion 2660, the light transport portion 2664 having a firstsegment 2664-1 and a second segment 2664-2; and a light extractionportion 2665 disposed to receive light from the light transport portion2664. The light 2638 received by the light insertion portion 2660propagates predominately along a first direction 2681, the lightreceived by the light transport portion 2683 propagates predominatelyalong a second direction 2683 in the first segment 2664-1, and the lightreceived by the light extraction portion propagates predominately alonga third direction 2685. A first included angle between the first andsecond directions 2681 and 2683 is at least 140, or at least 150degrees, or at least 160 degrees, or is about 180 degrees, and a secondincluded angle between the first and third directions is less than 40degrees, or less than 30 degrees, or less than 20 degrees. In theillustrated embodiment, the first included angle is about 180 degreesand the second included angle is about zero degrees. The first andsecond included angles can be changed by changing the orientation of thelight insertion portion 2660 and/or the orientation of the lightextraction portion 2685 such that one of both of the portions is tiltedfrom the x-y plane. The included angle between two directions refers tothe principle value of the inverse cosine (which is, by definition, in arange of zero to 180 degrees) of the dot product of the unit vectorsalong the two directions. For example, referring to FIG. 29, which is aschematic representation of an included angle between two directions,the inverse cosine of the dot product of unit vectors 2981 and 2985gives the angle φ which is the included angle between a first directionalong unit vector 2981 and a second direction along unit vector 2985.Since an included angle must be between zero and 180 degrees, specifyingan included angle as greater than 140 degrees is equivalent tospecifying the included angle as between 140 degrees and 180 degrees,for example.

The light transport portion 2664 is disposed to receive light from thelight insertion portion 2660 through a first fold 2671 and to transportthe light to the light extraction portion 2665 though a second fold2674. The second fold 2674 includes a first sub-fold 2674-1 and a secondsub-fold 2674-2.

FIG. 27 is a schematic cross-sectional view of light guide 2763 whichincludes a light insertion portion 2760 adapted to receive light 2738,and a light extraction portion 2765 disposed to receive light from thelight insertion portion 2760. The light extraction portion 2765 receiveslight from the light insertion portion 2760 through fold 2771. The lightreceived by the light insertion portion 2760 propagates predominatelyalong a first direction 2781, and the light received by the lightextraction portion 2765 propagates predominately along a seconddirection 2765. An included angle between the first direction 2781 andthe second direction 2785 is at least 120 degrees, or at least 140degrees, or at least 160 degrees. For example, the included angle may bein a range of 160 to 180 degrees, or may be about 180 degrees asillustrated. The light extraction portion 2765 may include a pluralityof light extraction features adapted to extract light from the lightextraction portion towards a projection lens system as illustrated inFIGS. 16A-16C, for example. An angle within 5 degrees of zero degreesmay be described as about zero degrees and an angle within 5 degrees of180 degrees may be described as about 180 degrees.

The light guides 2663 and 2763 each include a light insertion portionadapted to receive light; a light transport portion disposed to receivelight from the light insertion portion through a first fold; and a lightextraction portion disposed to receive light from the light transportportion through a second fold. In each case, the light extractionportion is spaced apart from and faces the light insertion portion. Insome embodiments, the light extraction portion and the light insertionportion may contact each other or may be separated by only a small gap.FIG. 28 is a schematic cross-sectional view of light guide 2863 whichincludes a light insertion portion 2860 and a light extraction portion2865 optically connected to each other through a fold 2871. The lightextraction portion 2865 may include a plurality of light extractionfeatures adapted to extract light from the light extraction portion 2865towards a projection lens system as illustrated in FIGS. 16A-16C, forexample. Light propagates in light insertion portion 2860 primarilyalong first direction 2881 and light propagates in light extractionportion 2865 primarily along second direction 2885. The included anglebetween the first and second directions 2881 and 2885 may be in at least140 degrees, for example.

In some embodiments, a light redirecting layer includes a concavesurface that is concave toward the pixelated light source with eachdifferent portion of the concave surface corresponding to a differentgroup of pixels in the pixelated light source. The portions of theconcave surface may be in one to one correspondence with the groups ofpixels. This is illustrated in FIG. 17 which is a schematic side view oflight emitting system 1732 including light redirecting layer 1750 andpixelated light source 1730. Light emitting system 1732 may be used forany of light emitting systems 132, 232, 332, 432, and 532, in opticalsystem 100, 200, 300, 400 and 500, respectively, for example. In theillustrated embodiment, light redirecting layer 1750 includes a singleoptical element having a concave surface 1758 which is concave towardslight redirecting layer 1730. Pixelated light source 1730 includes aplurality of pixels 1744 which includes a plurality of groups of pixelsincluding groups 1741 a, 1741 b, 1741 c, and 1741 d. Concave surface1758 includes a plurality of portions 1756 a, 1756 b, 1756 c, and 1756d. Each different portion corresponding to a different group of pixels.For example, light from group of pixels 1741 a may pass through portion1756 a of concave surface 1758 and may substantially not pass throughother portions of the concave surface 1758. This can be achieved placingthe pixels in close proximity to the concave surface 1758. Inembodiments where an LCD panel comprises the plurality of pixels, a thinouter glass layer may be used as described elsewhere herein in order toposition the light redirecting layer 1750 closer to the plurality ofpixels. In embodiments where an LCD panel comprises the plurality ofpixels, the light redirecting layer 1750 may be formed from an outerglass layer of the LCD panel as described elsewhere herein in order toposition the surface 1758 close to the plurality of pixels 1744. In someembodiments, when pixelated light source 1732 is used in an opticalsystem including a lens system, such as those including a partialreflector and a reflective polarizer as described elsewhere herein, anylight from a group of pixels that passes through any portion of concavesurface 1758 other than the portion corresponding to the group of pixelsmay be outside an acceptance angle of the lens system and therefore notutilized by the optical system.

FIG. 18 is a schematic cross-sectional view of light emitting system1832 including a liquid crystal display panel 1830, a backlight 1836,and a light redirecting layer 1850 having a concave light redirectingsurface 1858. Although a liquid crystal display panel is illustrated inFIG. 18, light redirecting layer 1850 may be used with other types ofpixelated displays, such as an OLED display, for example. Light emittingsystem 1832 may be used for any of light emitting systems 132, 232, 332,432, 532, in optical system 100, 200, 300, 400 and 500, respectively,for example. Liquid crystal display panel 1830 includes a plurality ofpixels 1844 disposed between first and second glass layers 1876 and1878. The plurality of pixels 1844 includes first pixel 1841 and secondpixel 1842. A first polarizer 1872 is disposed between the lightredirecting layer 1850 and the liquid crystal display panel 1830 and asecond polarizer 1873 is disposed between the liquid crystal displaypanel 1830 and the backlight 1836. The backlight 1836 may be an at leastpartially collimating backlight as described elsewhere herein. Lightemitting system 1832 is centered on an optical axis 1840. Lightredirecting layer 1850 is a single light redirecting element in theillustrated embodiment. Light redirecting layer 1850 includes a concavelight redirecting surface 1858 which is concave toward liquid crystalpanel 1830. Concave light redirecting surface 1858 includes firstportion 1856 adapted to receive light from first pixel 1841 and includessecond portion 1857 adapted to receive light from second pixel 1842. Insome embodiments, concave light redirecting surface 1858 includes aplurality of different portions with each different portion being in oneto one correspondence with a different pixel, or with a different groupof pixels, in the plurality of pixels 1844.

FIG. 19 is a schematic cross-sectional view of light emitting system1932 including a liquid crystal display panel 1930, a backlight 1936,and a light redirecting layer 1950 having a concave light redirectingsurface 1958. Liquid crystal display panel 1930 includes a plurality ofpixels 1944 disposed between first and second glass layers 1976 and1978. The light redirecting layer 1950 is formed from first glass layer1976 by, for example, etching the outer surface of the first glass layer1976 to form concave light redirecting surface 1958. Suitable glassetching methods that can be used to form concave light redirectingsurface 1958 are known in the art and are described, for example, inU.S. Pat. Pub. No. 2002/0079289 (Doh). Suitable glass etchants includehexafluorosilicic acid and hydrogen fluoride.

The plurality of pixels 1944 includes first pixel 1941 and second pixel1942. A first polarizer 1972 is disposed on concave light redirectingsurface 1958, and a second polarizer 1973 is disposed between the liquidcrystal display panel 1930 and the backlight 1936. The backlight 1936may be an at least partially collimating backlight as describedelsewhere herein. Light emitting system 1932 is centered on an opticalaxis 1940. Concave light redirecting surface 1958 includes first portion1956 adapted to receive light from first pixel 1941 and includes secondportion 1957 adapted to receive light from second pixel 1842. Asdescribed further elsewhere herein, in some embodiments, concave lightredirecting surface 1958 includes a plurality of different portions witheach different portion being in one to one correspondence with adifferent pixel, or with a different group of pixels, in the pluralityof pixels 1944. Light emitting system 1932 may be used for any of lightemitting systems 132, 232, 332, 432, 532, in optical system 100, 200,300, 400 and 500, respectively, for example.

In some embodiments of light emitting system 1832 or 1932, eachdifferent portion of the concave light redirecting surface correspondsto a different group of pixels in the plurality of pixels and receives afirst diverging light emitted by a pixel in the group of pixels having afirst cone angle and transmits the received light as a second diverginglight having a second cone angle less than the first cone angle. In someembodiments, light from a pixel in a group of pixels is eithersubstantially not transmitted through any portion of the lightredirecting layer not corresponding to the group of pixels or is at mostpartially transmitted through a portion of the light redirecting layernot corresponding to the group of pixels in a direction that is notwithin an acceptance angle of a lens system adapted to receive lightfrom the light emitting system.

FIG. 20 is a schematic cross-sectional view of light emitting system2032 including a plurality of light redirecting elements which includeslight redirecting element 2056 and 2057, a liquid crystal display panel2030 having a plurality of discrete spaced apart pixels 2044 provided bya liquid crystal layer between first and second glass layers 2076 and2078. The first glass layer 2076 may have a reduced thickness comparedto conventional LCD displays or compared to the second glass layer 2078in order to position the light redirecting elements 2056 and 2057 closerto the apertures defining the plurality of pixels 2044. Although aliquid crystal display panel is illustrated in FIG. 20, lightredirecting elements 2056 and 2057 may be used with other types ofpixelated displays, such as an OLED display, for example. The liquidcrystal display panel 2030 is disposed between first and secondpolarizers 2072 and 2073 and is illuminated by backlight 2036 which maybe an at least partially collimating backlight as described elsewhereherein. Each light redirecting element may correspond to a group ofpixels in the plurality of pixels, where the group may be a single pixelor a plurality of pixels. Light redirecting elements may be included forsome, for most, or for all of the pixels. For example, light redirectingelements may be included for all pixels except for pixels located nearan optical axis of the light emitting system 2032 or of an opticalsystem including a lens system and the light emitting system 2032. Lightemitting system 2032 may be used for any of light emitting systems 132,232, 332, 432, 532, in optical system 100, 200, 300, 400 and 500,respectively, for example. Each of the light redirecting elements may beprismatic elements and may optionally include one or more curvedsurfaces. In alternate embodiments, a plurality of microlenses may beused in place of some or all of the prismatic elements. In still otherembodiments, a light redirecting layer comprising a Fresnel lens may beused in place of individual light redirecting elements. This isillustrated in FIG. 21.

FIG. 21 is a cross-sectional view of light emitting system 2132including light redirecting layer 2150 and liquid crystal display panel2130 which includes a plurality of discrete spaced apart pixels 2144.Although a liquid crystal display panel is illustrated in FIG. 21, lightredirecting layer 2150 may be used with other types of pixelateddisplays, such as an OLED display, for example. Liquid crystal panel2130 is disposed between first and second polarizers 2172 and 2173 andilluminated by backlight 2136, which may be an at least partiallycollimating backlight as described elsewhere herein. Light redirectinglayer 2150 includes light redirecting elements 2156 and may be a Fresnellens or may be a blazed diffraction grating. In some embodiments, atleast some of the light redirecting element 2156 are concentric rings.Each light different redirecting element 2156 may correspond to adifferent group of pixels in the plurality of discrete spaced apartpixels 2144. For example, if a light redirecting element is a concentricring shaped element, the group of pixels corresponding the lightredirecting element may be the plurality of pixels disposed under theconcentric ring. In still other embodiments, light redirecting layer2150 may be replaced by other types of light redirecting elements. Forexample, light redirecting layer 2150 may be a holographic opticalelement.

Light emitting system 2132 may be used for any of light emitting systems132, 232, 332, 432, 532, in optical system 100, 200, 300, 400 and 500,respectively, for example.

FIG. 22 is a schematic cross-sectional view of light emitting system2232 including liquid crystal display panel 2230 which includes aplurality of pixels 2244 and first and second glass layers 2276 and2278. A plurality of lenses including lenses 2256 and 2257 are formed infirst glass layer 2276. The lenses may be formed by etching the firstglass layer 2276 and filling the etched out regions with a materialhaving a refractive index different than that of the first glass layer2276. For example, a higher refractive index material may be used inorder to reduce a divergence angle of light emitted by a correspondingpixel. Suitable high index materials include polymeric materials filledwith high refractive index nanoparticles such as those described in U.S.Pat. No. 8,343,622 (Liu et al.) which is hereby incorporated herein tothe extent that it does not contradict the present description. Eachdifferent lens in the plurality of lenses may correspond to a differentgroup of pixels in the plurality of pixels. Each group of pixels may bea single pixel or may include a plurality of pixels. Light emittingsystem 2232 may be used for any of light emitting systems 132, 232, 332,432, 532, in optical system 100, 200, 300, 400 and 500, respectively,for example.

The light redirecting layer or light redirecting elements of any of thelight emitting systems 1732, 1832, 1932, 2032, 2132 and 2232, may beadapted to bend light output from at least one pixel, or of a majorityof the pixels, toward or away from an optical axis of the lightredirecting layer or light redirecting elements or toward or away froman optical axis of a display system incorporating a lens system and thelight redirecting layer or elements.

An alternative to including a light redirecting layer on a display panelis to include a light redirecting layer on a lens disposed to receivelight from a display panel. FIG. 23 is a schematic cross-sectional viewof lens system 2319 including first and second optical lenses 2310 and2320. First optical lens 2310 includes opposing first and second majorsurfaces 2314 and 2316, the first major surface 2314 being an innermajor surface and the second major surface 2316 being an outer majorsurface. Second optical lens 2320 includes opposing first and secondmajor surfaces 2324 and 2326. Lens system 2319 includes a partialreflector which may be disposed on first major surface 2314 of firstlens 2310. Lens system 2319 also includes a reflective polarizerconfigured to substantially transmit light having a first polarizationstate and substantially reflect light having an orthogonal secondpolarization state. The reflective polarizer is disposed adjacent to andspaced apart from the partial reflector and may be disposed on thesecond lens 2320. In some embodiments, the reflective polarizer isdisposed on second major surface 2326. In some embodiments, aquarter-wave retarder is disposed on the reflective polarizer. Thepartial reflector may have an average optical reflectance of at least30% in a desired plurality of wavelengths as described elsewhere herein.

The second major surface 2316 of the first optical lens 2310 includes aplurality of light redirecting elements 2350 including light redirectingelements 2356 and 2357. Each light redirecting element is adapted toreceive a first cone of light and transmit the received light as asecond cone of light towards the partial reflector. For example lightredirecting element 2356 is adapted to receive first cone of light 2339and transmit the received light as second cone of light 2349. Asdescribed further elsewhere herein, each light redirecting element maybe adapted to change one or both of a divergence angle and a central raydirection of the received cone of light. Lens system 2319 may be used inplace of lens systems 119 or 219 in the optical systems 100 or 200,respectively, for example.

The reflective polarizer included in lens system 2319 may be curvedabout one or two orthogonal axes. In some embodiments, the reflectivepolarizer is a multilayer polymeric film and in some embodiments thereflective polarizer is a thermoformed or pressure-formed multilayerreflective polarizer such as APF as described elsewhere herein.

In some embodiments, a brightness of a display system including apixelated light emitting system and lens system 2319 disposed to receivelight emitted by the pixelated system at an exit pupil of the displaysystem is at least 30 percent higher than that of an otherwiseequivalent display system not including the plurality of lightredirecting elements 2350. In some embodiments, the brightness of thedisplay system at the exit pupil is at least 100 percent higher, or atleast 200 percent higher, or at least 300 percent higher than that ofthe otherwise equivalent display system.

FIG. 24 is a schematic cross-sectional view of a portion of a displaysystem 2400 including a light emitting system 2432 which includes aplurality of light emitting pixels 2444. Each light emitting pixelincludes an optional optically transparent first light redirectingelement 2456 having an average optical transmittance of at least 50% ina desired plurality of wavelengths, an optically reflecting second lightredirecting element 2457 concave toward the first light redirectingelement 2456 and having an average optical reflectance of at least 50%in the desired plurality of wavelengths, and a light emitting material2441 disposed between the first and second light redirecting elements2456 and 2457. The light emitting material 2441 may be included in adisplay panel 2430 which may be an at least partially transmissive OLEDdisplay panel, for example. The display panel 2430 is shown as asubstantially planar panel in FIG. 24, but in other embodiments thedisplay panel may be curved (see, e.g., FIG. 1B) or may include aplurality of planar portions not all in a same plane (see, e.g., FIG.1C). In some embodiments, a center 2442 of the second light redirectingelement 2457 lies within the light emitting material 2441. For example,the second light redirecting element 2457 may have a concave reflectivesurface having a center of curvature or a focal point that lies withinthe light emitting material 2441. In some embodiments, light emitted bythe light emitting material 2441 is substantially collimated by thefirst and second light redirecting elements 2456 and 2457. In someembodiments, the optional first light redirecting element 2456 isomitted and light emitted by the light emitting material 2441 issubstantially collimated by the second light redirecting element 2457.For example, light emitting material in the panel 2430 may emit adiverging first cone of light 2439 which is reflected from a concavesecond light redirecting element and transmitted through a first lightredirecting element as substantially collimated light 2449.

Display system 2400 may further include a lens system, such as lenssystems 119 or 219, for example, disposed to receive light from thelight emitting system 2432 and transmit at least a portion of thereceived light to an exit pupil of the display system 2400.

Optical transmittance or reflectance of various components (e.g.,partial reflector, quarter-wave retarder, transmissive optical elements,and reflective optical elements) may be specified by an average in adesired or predetermined plurality of wavelengths. The desired orpre-determined plurality of wavelengths may, for example, be anywavelength range in which the optical system is designed to operate. Thepre-determined or desired plurality of wavelengths may be a visiblerange, and may for example, be the range of wavelengths from 400 nm to700 nm. In some embodiments, the desired or pre-determined plurality ofwavelengths may be an infrared range or may include one or more ofinfrared, visible and ultraviolet wavelengths. In some embodiments, thedesired or pre-determined plurality of wavelengths may be a narrowwavelength band, or a plurality of narrow wavelength bands, and thepartial reflector, for example, may be a notch reflector. In someembodiments, the desired or pre-determined plurality of wavelengthsinclude at least one continuous wavelength range that has a full widthat half maximum of no more than 100 nm, or no more than 50 nm.

Any of the optical systems of the present description may be used in adevice such as a head-mounted display (e.g., a virtual reality display).FIG. 25 is a schematic top view of head-mounted display 2590 including aframe 2592, first and second display portions 2594 a and 2594 b whichmay include any of the optical systems of the present description. Inthe illustrated embodiment, first display portion 2594 a includes lenssystem 2519 a and light emitting system 2532 a and display portion 2594b includes lens system 2519 b and light emitting system 2532 b. Each oflens systems 2519 a and 2519 b may include a reflective polarizer and apartial reflector as described elsewhere herein. Each of light emittingsystems 2532 a and 2532 b may include a plurality of pixels and a lightredirecting layer and/or an at least partially collimating backlight asdescribed elsewhere herein. In some embodiments, lens systems 2519 a and2519 b are centered on an optical axis (e.g., an axis parallel to thez-axis in FIG. 25) and light emitting systems 2532 a and 2532 b aredisposed at an obtuse angle relative to the corresponding optical axis.In other embodiments, the light emitting systems 2532 a and 2532 b aredisposed at right angles to the corresponding optical axis and may becentered on the corresponding optical axis. Light redirecting layers ofthe light emitting systems 2532 a and 2532 b may redirect light outputby the corresponding pixels so that it is within the acceptance angle ofthe corresponding lens system. In embodiments where the light emittingsystem is disposed at an obtuse angle to the optical axis of a lenssystem, the light redirecting elements of the light emitting system mayinclude a curved surface, such as curved surface 1131 c, which isasymmetric about the optical axis.

EXAMPLES Example 1

A folded optic lens system with elements described in the followingtable was modeled using Zemax 15 lens design software.

Thick- Semi- Surface Radius ness Diameter Type (mm) (mm) Material (mm)Conic OB Standard Infinity Infinity NA Infinity 0.000 ST StandardInfinity 10.000 NA 3.542 0.000 2 Even 36.671 5.000 Polycar- 15.000−20.921 Asphere bonate 3 Even −66.536 2.261 NA 15.391 13.841 Asphere 4Even −37.346 −2.261 Mirror 15.589 2.644 Asphere 5 Even −66.536 2.261Mirror 14.989 13.841 Asphere 6 Even −37.346 6.000 E48R 14.931 2.644Asphere 7 Even −7.233 6.001 NA 15.167 −3.173 Asphere IM StandardInfinity NA NA 12.205 0.000

In the above table, OB refers to the object and the surfaces are listedorder from the stop surface (ST) to the image surface (IM). The asphericpolynomial coefficients were taken to be zero except for surface 7 whichhad second, fourth, sixth, eight, and tenth order coefficients of 0.000,−2.805×10⁻⁵, 1.232×10⁻⁷, −1.936×10⁻¹⁰, and −3.088×10⁻¹³, respectively.

The lens was imported into LightTools, where a display plane was createdwith a central and peripheral emissive element. Each element wasimmersed in an NBK7 lens with a 0.1 mm diameter and a 0.05 mm radius.The emissive elements were designed to have a 0.004 mm square emissivearea. Placement of the lens relative to the emissive element wasoptimized so as to provide the best combination of uniformity andbrightness at the pupil. The near eye display with the microlens arraywas 8.1 times brighter than without the lens array (710 percent increasein brightness).

Example 2

An optical system similar to optical system 200 was modeled using raytracing as follows. Optical stack 210 included a quarter wave retarderon the outer surface (surface facing panel 232) of lens 212 and partialreflector on the inner surface (surface facing exit pupil 235) of lens212. Optical stack 220 included a linear polarizer on the outer surface(surface facing lens 212) of lens 222 and included a quarter waveretarder disposed on the linear polarizer. The quarter wave retarderswere modeled as ideal retarders, the partial reflector was modeled ashaving a transmissivity of 50 percent and a reflectivity of 50 percent,and the linear polarizer was modeled as having a 1 percenttransmissivity and a 99 percent reflectivity for light polarized along alinear block axis, and a 99 percent transmissivity and a 1 percentreflectivity for light polarized along an orthogonal linear pass axis.The lenses were as specified in the following table:

Thick- Semi- Surface Radius ness Diameter Type (mm) (mm) Material (mm)Conic OB Standard Infinity Infinity NA Infinity 0.0000000 ST StandardInfinity 15.000 NA 3.424 0.0000000 2 Even −23.172 2.500 Polycar- 12.5000.0000000 Asphere bonate 3 Even −18.852 4.691 NA 13.316 0.5582269Asphere 4 Standard Infinity 0.000 NA 21.709 0.0000000 5 Even −19.441−4.691 Mirror 15.345 −9.5827826 Asphere 6 Even −18.852 4.691 Mirror12.193 0.5582269 Asphere 7 Even −19.441 2.000 E48R 15.500 −9.5827826Asphere 8 Even −19.441 1.820 NA 15.500 −9.5827826 Asphere 9 StandardInfinity 0.281 PMMA 14.520 0.0000000 10 Standard Infinity 0.010 NA14.547 0.0000000 11 Standard Infinity 0.700 N-BK7 14.548 0.0000000 12Standard Infinity 0.000 NA 14.620 0.0000000 IM Standard Infinity NA NA14.000 0.0000000The second through eight order aspheric polynomial coefficients used forthe lens surfaces are given in the following table:

2nd Order 4th Order 6th Order 8th Order OB NA NA NA NA ST NA NA NA NA 20.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 3 0.0000E+00 1.2455E−051.3936E−07 1.8601E−09 4 NA NA NA NA 5 0.0000E+00 −1.4624E−04 9.5699E−07−6.0196E−09 6 0.0000E+00 1.2455E−05 1.3936E−07 1.8601E−09 7 0.0000E+00−1.4624E−04 9.5699E−07 −6.0196E−09 8 0.0000E+00 −1.4624E−04 9.5699E−07−6.0196E−09 9 NA NA NA NA 10  NA NA NA NA 11  NA NA NA NA 12  NA NA NANA IM NA NA NA NAThe tenth and higher order aspheric polynomial coefficients used for thelens surfaces are given in the following table:

10th Order 12th Order 14th Order (mm⁻⁹) (mm⁻¹¹) (mm⁻¹³) OB NA NA NA STNA NA NA 2 0.0000E+00   0.0000E+00 0.0000E+00 3 2.4079E−11 −1.2664E−132.8533E−16 4 NA NA NA 5 2.3733E−11 −5.3312E−14 4.9018E−17 6 2.4079E−11−1.2664E−13 2.8533E−16 7 2.3733E−11 −5.3312E−14 4.9018E−17 8 2.3733E−11−5.3312E−14 4.9018E−17 9 NA NA NA 10  NA NA NA 11  NA NA NA 12  NA NA NAIM NA NA NA

The display panel 235 was modeled as producing a checker-board patternof bright and dark squares, each squares having a dimension of 6 mm×6mm. The display panel had dimensions of 2.4 cm×2.4 cm. The light outputwas modeled as having a central ray normal to the surface of the displaypanel and having a cone angle of 5 degrees half width at half maximum(HWHM). This was chosen to simulate a display panel with a partiallycollimating backlight or with a light redirecting layer that partiallycollimates the light output. For comparison, a conventional displaypanel having a cone angle of 35 degrees HWHM was also modeled. Receiverswere position an exit pupil 235. The contrast ratio was calculated asthe average power of received at a bright square to the average powerreceived at a dark square. For the partially collimated (5 degree HWHM)case, the contrast ratio was determined to be 747, while for theconventional case (35 degree HWHM), the contrast ratio was determined tobe 100.

Example 3

The relative efficiency of optical system 1600 (depicted in FIG. 16A)and similar optical systems with backlight 1636 replaced with differentbacklight units were calculated. The relative efficiency of the opticalsystem utilizing a backlight unit with a Lambertian output was definedto be unity. The relative efficiency of other optical systems was thendefined as the ratio of the brightness at the exit pupil 1635 of theoptical system to the brightness at the exit pupil 1635 of the opticalsystem with the backlight unit having a Lambertian output. When thebacklight unit included one Brightness Enhancement Film (BEF availablefrom 3M Company, St. Paul, Minn.), the output from the backlight unithad a Full-Width and Half Maximum (FWHM) in a horizontal direction(width direction of the display) of 44 degrees and in a verticaldirection (height direction of the display) of 80 degrees and theoptical system had a relative efficiency of 1.4 (40 percent increase inbrightness). When the backlight unit included two crossed BEFs, theoutput from the backlight unit had a FWHM of 44 degrees in both thehorizontal and vertical directions and the optical system had a relativeefficiency of 1.6 (60 percent increase in brightness). When thebacklight unit included a structured surface 1667 adapted to provide ahigh degree of collimation in a direction normal to the display (in theminus z-direction), the output from the backlight unit had a FWHM of 16degrees in the horizontal direction and 12 degrees in the verticaldirection and the optical system had a relative efficiency of 2.4 (140percent increase in brightness). When the backlight unit included astructured surface 1667 adapted to provide a high degree of collimationin directions turned towards the lens system 1619, the output from thebacklight unit had a FWHM of 12 degrees in the horizontal direction and11 degrees in the vertical direction and the optical system had arelative efficiency of 3 (200 percent increase in brightness). Theresults are summarized in the following table.

FWHM-Horizontal FWHM-Vertical Relative Backlight Unit (degrees)(degrees) Efficiency Lambertian 90 90 1 BEF 44 80 1.4 Crossed BEF 44 441.6 Collimated 16 12 2.4 Collimated and 12 11 3 angle optimizedThe following is a list of exemplary embodiments of the presentdescription.Embodiment 1 is a display system, comprising:an imager for forming an image, the imager comprising a plurality ofdiscrete spaced apart pixels; anda projection lens system for projecting the image formed by the imager,wherein for each pixel in the plurality of pixels, the imager isconfigured to emit a cone of light having a central ray, the central rayhaving a direction that varies with location of the pixel in the imager,the variation increasing a brightness of an image projected through theprojection lens system by at least 30 percent.Embodiment 2 is the display system of Embodiment 1, wherein theprojection lens system comprises a folded optical system.Embodiment 3 is the display system of Embodiment 2, wherein the foldedoptical system comprises:a first partial reflector having an average optical reflectance of atleast 30% in a desired plurality of wavelengths; anda second partial reflector adjacent to and spaced apart from the firstpartial reflector.Embodiment 4 is the display system of Embodiment 3, wherein the secondpartial reflector is a reflective polarizer substantially transmittinglight having a first polarization state and substantially reflectinglight having an orthogonal second polarization state.Embodiment 5 is the display system of Embodiment 3, wherein the secondpartial reflector has an average optical reflectance of at least 30% inthe desired plurality of wavelengths.Embodiment 6 is the display system of Embodiment 1, wherein theprojection lens system comprises a refractive optical system.Embodiment 7 is the display system of Embodiment 1, wherein theprojection lens system has an acceptance angle and the variation in thecentral ray direction increases light emitted by the imager that iswithin the acceptance angle by at least 30 percent.Embodiment 8 is the display system of Embodiment 1, wherein theprojection lens system has an optical axis and an angle between thecentral ray and the optical axis varies with location of the pixel inthe imager.Embodiment 9 is the display system of Embodiment 1, wherein imager has asurface normal and an angle between the central ray and the surfacenormal varies with location of the pixel in the imager.Embodiment 10 is the display system of Embodiment 1, wherein the imageris substantially planar.Embodiment 11 is the display system of Embodiment 1, wherein the imagerincludes a plurality of planar portions disposed at oblique anglesrelative to one another.Embodiment 12 is the display system of Embodiment 1, wherein the imageris curved.Embodiment 13 is the display system of Embodiment 1, wherein theprojection lens system has a largest lateral optically active dimensionless than one half of a largest optically active dimension of theimager.Embodiment 14 is the display system of Embodiment 1 further comprising alight guide having a light insertion portion and a light extractionportion in optical communication with the light insertion portion andwith the imager.Embodiment 15 is the display system of Embodiment 14, wherein the lightinsertion portion and the light extraction portion are spaced apartalong an optical axis of the lens system.Embodiment 16 is the display system of Embodiment 15, wherein the lightguide further comprises a light transport portion configured to receivelight from the light insertion portion and transport the light to thelight extraction portion.Embodiment 17 is the display system of Embodiment 16, wherein theoptical axis intersects each of the light insertion portion, the lighttransport portion and the light extraction portion.Embodiment 18 is the display system of Embodiment 14, wherein the lightguide is folded such that the light extraction portion faces the lightinsertion portion.Embodiment 19 is the display system of Embodiment 14, wherein lightreceived by the light insertion portion propagates predominately along afirst direction, the light received by the light extraction portionpropagating predominately along a second direction, and an includedangle between the first and second directions is less than 40 degrees orgreater than 140 degrees.Embodiment 20 is the display system of Embodiment 14, wherein the imagercomprises a transmissive spatial light modulator disposed proximate thelight extraction portion opposite the light insertion portion.Embodiment 21 is the display system of Embodiment 14, wherein the imagercomprises a reflective spatial light modulator disposed between thelight extraction portion and the light insertion portion.Embodiment 22 is a display system comprising:a projection lens system having one or more lenses centered on anoptical axis;a light guide comprising:

-   -   a light insertion portion adapted to receive light;    -   a light transport portion disposed to receive light from the        light insertion portion; and    -   a light extraction portion disposed to receive light from the        light transport portion, the light extraction portion configured        to provide a light output central ray direction having an angle        with respect to the optical axis that varies with location on an        output surface of the light extraction portion, the light        extraction portion being separated from the light insertion        portion along the optical axis forming a space between the light        extraction portion and the light insertion portion; and        a spatial light modulator in optical communication with the        light extraction portion,        wherein the light guide is folded such that the light extraction        portion faces the light insertion portion.        Embodiment 23 is the display system of Embodiment 22, wherein        the optical axis intersects the light insertion portion and the        light extraction portion.        Embodiment 24 is the display system of Embodiment 23, wherein        the optical axis intersects the light transport portion.        Embodiment 25 is the display system of Embodiment 22, wherein        the spatial light modulator is disposed between the lens system        and the light extraction portion.        Embodiment 26 is the display system of Embodiment 25, wherein        the spatial light modulator is a transmissive liquid crystal        panel.        Embodiment 27 is the display system of Embodiment 25, wherein a        reflector is disposed in the space between the light extraction        portion and the light insertion portion.        Embodiment 28 is the display system of Embodiment 22, wherein        the spatial light modulator is disposed in the space between the        light extraction portion and the light insertion portion.        Embodiment 29 is the display system of Embodiment 28, wherein        the spatial light modulator is a reflective liquid crystal        panel.        Embodiment 30 is the display system of Embodiment 29, wherein        the reflective liquid crystal panel is a Liquid Crystal on        Silicon (LCoS) panel.        Embodiment 31 is the display system of Embodiment 22, wherein        the projection lens system comprises a folded optical system.        Embodiment 32 is the display system of Embodiment 31, wherein        the projection lens system comprises:        a partial reflector having an average optical reflectance of at        least 30% in a desired plurality of wavelengths; and        a reflective polarizer substantially transmitting light having a        first polarization state and substantially reflecting light        having an orthogonal second polarization state.        Embodiment 33 is the display system of Embodiment 22, wherein        the projection lens system is a refractive optical system.        Embodiment 34 is the display system of Embodiment 22, wherein        the optical lens system has a largest lateral optically active        dimension less than one half of a largest lateral optically        active dimension of the spatial light modulator.        Embodiment 35 is a display system comprising:        a projection lens system having one or more lenses and having a        largest lateral optically active dimension; an imager having a        largest lateral optically active dimension, an image formed by        the imager projected by the projection lens system;        a light guide for receiving light from a light source and        comprising a light extraction portion disposed between the        projection lens system and the imager, the light extraction        portion comprising a plurality of discrete spaced apart light        extraction features for extracting and directing the received        light toward the imager,        wherein the largest lateral optically active dimension of the        projection lens system is no more than 80 percent of the largest        lateral optically active dimension of the imager.        Embodiment 36 is the display system of Embodiment 35, wherein        the largest lateral optically active dimension of the projection        lens system is no more than 60 percent of the largest lateral        optically active dimension of the imager.        Embodiment 37 is the display system of Embodiment 35, wherein        the largest lateral optically active dimension of the projection        lens system is no more than 50 percent of the largest lateral        optically active dimension of the imager.        Embodiment 38 is the display system of Embodiment 35, wherein        the largest lateral optically active dimension of the projection        lens system is no more than 40 percent of the largest lateral        optically active dimension of the imager.        Embodiment 39 is the display system of Embodiment 35, wherein        the light guide further comprises a light insertion portion in        optical communication with the light extraction portion.        Embodiment 40 is the display stem of Embodiment 39, where the        light guide is folded such that the light insertion portion        faces the light extraction portion.        Embodiment 41 is the display system of Embodiment 39, wherein        the light guide further comprises a light transport portion        disposed to receive light from the light insertion portion        through a first fold and to transport the light to the light        extraction portion though a second fold.        Embodiment 42 is the display system of Embodiment 41, wherein        the lens has an optical axis, the optical axis intersecting the        light insertion portion and the light extraction portion.        Embodiment 43 is the display system of Embodiment 42, wherein        the optical axis intersects the light transport portion.        Embodiment 44 is the display system of Embodiment 39, wherein        the imager is disposed between the light extraction portion and        the light insertion portion.        Embodiment 45 is the display system of Embodiment 44, wherein        the spatial light modulator is a reflective liquid crystal        panel.        Embodiment 46 is the display system of Embodiment 45, wherein        the reflective liquid crystal panel is a Liquid Crystal on        Silicon (LCoS) panel.        Embodiment 47 is the display system of Embodiment 38, wherein        the light insertion portion comprises an optical element        configured to at least partially collimate light injected into        the light insertion portion.        Embodiment 48 is a light guide comprising:        a light insertion portion adapted to receive light;        a light transport portion disposed to receive light from the        light insertion portion through a first fold; and        a light extraction portion disposed to receive light from the        light transport portion through a second fold, wherein the light        extraction portion is spaced apart from and faces the light        insertion portion.        Embodiment 49 is the light guide of Embodiment 48, wherein the        light insertion portion comprises an optical element configured        to at least partially collimate light received into the light        insertion portion.        Embodiment 50 is the light guide of Embodiment 48, wherein the        light extraction portion has opposing first and second major        surfaces, the first major surface comprising a plurality of        discrete spaced apart light extraction features disposed to        extract light from the light extraction portion through the        second major surface toward the light insertion portion.        Embodiment 51 is the light guide of Embodiment 50, wherein a        reflective polarizer is disposed on the first major surface.        Embodiment 52 is the light guide of Embodiment 48, further        comprising a reflector disposed between the light extraction        portion and the light insertion portion, the reflector receiving        light extracted from the light extraction portion and reflecting        the light back through the light extraction portion.        Embodiment 53 is a display system comprising the light guide of        Embodiment 52 and a transmissive spatial light modulator        disposed to receive the light reflected from the reflector        through the light extraction portion.        Embodiment 54 is a display system comprising the light guide of        Embodiment 48 and a reflective spatial light modulator disposed        between the light extraction portion and the light insertion        portion.        Embodiment 55 is a light guide comprising:        a light insertion portion adapted to receive light, the light        received by the light insertion portion propagating        predominately along a first direction;        a light transport portion disposed to receive light from the        light insertion portion, the light transport portion having a        first segment, the light received by the light transport portion        propagating predominately along a second direction in the first        segment; and        a light extraction portion disposed to receive light from the        light transport portion, the light received by the light        extraction portion propagating predominately along a third        direction,        wherein a first included angle between the first and second        directions is at least 140 degrees and a second included angle        between the first and third directions is less than 40 degrees.        Embodiment 56 is the light guide of Embodiment 55, wherein the        first included angle is at least 160 degrees and the second        included angle is less than 20 degrees.        Embodiment 57 is the light guide of Embodiment 55, wherein the        light transport portion receives light from the light insertion        portion through a first fold and the light extraction portion        receives light from the light transport portion through a second        fold.        Embodiment 58 is the light guide of Embodiment 55, wherein the        light extraction portion has opposing first and second major        surfaces, the first major surface comprising a plurality of        discrete spaced apart light extraction features disposed to        extract light from the light extraction portion through the        second major surface toward the light insertion portion.        Embodiment 59 is a display system comprising the light guide of        Embodiment 55 and a transmissive spatial light modulator        disposed proximate the light extraction portion opposite the        light insertion portion.        Embodiment 60 is a display system comprising the light guide of        Embodiment 55 and a reflective spatial light modulator disposed        between the light extraction portion and the light insertion        portion.        Embodiment 61 is a display system comprising:        a projection lens system;        a light guide comprising:    -   a light insertion portion adapted to receive light, the light        received by the light insertion portion propagating        predominately along a first direction;    -   a light extraction portion disposed to receive light from the        light insertion portion, the light received by the light        extraction portion propagating predominately along a second        direction, an included angle between the first direction and the        second direction being at least 120 degrees,        wherein the light extraction portion includes a plurality of        light extraction features adapted to extract light from the        light extraction portion towards the projection lens system.        Embodiment 62 is the display system of Embodiment 61, wherein        the included angle is at least 140 degrees.        Embodiment 63 is the display system of Embodiment 61, wherein        the included angle is at least 160 degrees.        Embodiment 64 is the display system of Embodiment 61, wherein        the included angle is about 180 degrees.        Embodiment 65 is the display system of Embodiment 61, wherein        the light extraction portion receives light from the light        insertion portion through a fold.        Embodiment 66 is the display system of Embodiment 61, wherein        the light extraction portion faces the light insertion portion.        Embodiment 67 is the display system of Embodiment 61, further        comprising a spatial light modulator in optical communication        with the light extraction portion.        Embodiment 68 is the display system of Embodiment 61, wherein        the spatial light modulator is disposed between the projection        lens system and the spatial light modulator.        Embodiment 69 is the display system of Embodiment 61, wherein        the light extraction portion is disposed between the spatial        light modulator and the projection lens system.        Embodiment 70 is the display system of Embodiment 61, wherein        the projection lens system comprises a folded optical system.        Embodiment 71 is the display system of Embodiment 61, wherein        the projection lens system comprises a refractive optical        system.

Related optical systems are described in the following U.S. patentapplication which is hereby incorporated herein by reference in itsentirety: OPTICAL SYSTEM (Ser. No. 62/347,650) filed on an even dateherewith.

Descriptions for elements in figures should be understood to applyequally to corresponding elements in other figures, unless indicatedotherwise. Although specific embodiments have been illustrated anddescribed herein, it will be appreciated by those of ordinary skill inthe art that a variety of alternate and/or equivalent implementationscan be substituted for the specific embodiments shown and describedwithout departing from the scope of the present disclosure. Thisapplication is intended to cover any adaptations or variations of thespecific embodiments discussed herein. Therefore, it is intended thatthis disclosure be limited only by the claims and the equivalentsthereof.

What is claimed is:
 1. A display system, comprising: an imager forforming an image, the imager comprising a plurality of discrete spacedapart pixels; a projection lens system centered on an optical axis forprojecting the image formed by the imager; and a light guide having alight extraction portion configured to provide a light output centralray direction having an angle with respect to the optical axis thatvaries with location on an output surface of the light extractionportion, the light extraction portion being configured to extract lighttowards the imager, the imager being configured to receive the extractedlight and reflect an imaged light back through the light extractionportion towards the projection lens system, wherein for each pixel inthe plurality of pixels, the imager is configured to receive light fromthe light guide and emit a cone of light having a central ray, thecentral ray having a direction that varies with location of the pixel inthe imager, the variation increasing a brightness of an image projectedthrough the projection lens system by at least 30 percent.
 2. Thedisplay system of claim 1, wherein the projection lens system comprisesa folded optical system.
 3. The display system of claim 2, wherein thefolded optical system comprises: a first partial reflector having anaverage optical reflectance of at least 30% in a desired plurality ofwavelengths; and a second partial reflector adjacent to and spaced apartfrom the first partial reflector.
 4. The display system of claim 3,wherein the second partial reflector is a reflective polarizersubstantially transmitting light having a first polarization state andsubstantially reflecting light having an orthogonal second polarizationstate.
 5. The display system of claim 3, wherein the second partialreflector has an average optical reflectance of at least 30% in thedesired plurality of wavelengths.
 6. The display system of claim 1,wherein the projection lens system comprises a refractive opticalsystem.
 7. The display system of claim 1, wherein the projection lenssystem has an acceptance angle and the variation in the central raydirection increases light emitted by the imager that is within theacceptance angle by at least 30 percent.
 8. The display system of claim1, wherein the projection lens system has a largest lateral opticallyactive dimension less than one half of a largest optically activedimension of the imager.